
No, 8984 





-^^^^ 



x^^^^ * 



0^00-,,% .^*\c^%^<L /..i^>>o /\c:,;l%\ --o^ 














/% 



•V. -"- .%>" ... V '" 






^^'^'^^. ^ 





^ o 































^a"^' Mi£^. V./^ *^^»'"' '"^^ -^^ ^^^ 



).♦ -^ />> 
















-^^^^ 



65> »^- 




' '^. 



^^.'^'^ 



* .♦'> 


















/.:^;fe%\. .>° .^^ °-.. ./Vi-i^'X .co^.^;:."°o ./\^^;^/\ co^ 








f 




°^ ^^<^ 

























,*^'v 













0^ "^o. *.-r.T^- ^ 



** -Jy^ ^<* 





,V 





















**„ ..** .'^-. *^^^# /^ \/ ..Jfe-, ^^^^^* 








v.^' 

















,'. -^^0^ -."-...^^Bl" '^^.^y :'£Sm>^\ ^^M.^ o^^m^'" V..-^' 



^oV 













^oV 







"^Cf^^^ 





















r 






^* ^ %> -: 



'•1^^^ 







<*. c"^ »'^l^'. ' t.. A^ ^ /^'^^Ao^ "^^^ c'^^ ^^-Sl^'. ' ^ A-^ ' ♦tr(\'^^A- "^^ c;^*" »'^lg»Si'". 't.. .^^ 



.<^v. 











L ' » _ •<$*. 






^v^-*- 

/% 



IC 


8984 



f: 



0' 



Bureau of Mines Information Circular/1984 




Selected Pneumatic Gunites for Use 
in Underground Mining: A Comparative 
Engineering Analysis 



By Gary W. Krantz 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8984 

H 

Selected Pneumatic Gunites for Use 
in Underground Mining: A Comparative 
Engineering Analysis 

By Gary W. Krantz 




UNITED STATES DEPARTMENT OF THE INTERIOR 
William P. Clark, Secretary 

BUREAU OF MINES 
Robert C. Norton, Director 




V 



A 



< 



.VX^# 



k 



^' 





UNIT OF MEASUREMENT 


ABBREVIATIONS 


USED IN THIS REPORT 


A 


angstrom 


lb/gal 


pound per gallon 


"C 


degree Celsius 


Ib/h 


pound per hour 


cm 


centimeter 


lb/yd3 


pound per cubic yard 


cm2 


square centimeter 


m2/kg 


square meter per kilogram 


cm3 


cubic centimeter 


m^/min 


cubic meter per minute 


cm^/min 


cubic centimeter 


mg 


milligram 




per minute 


mg/m^ 


milligram per cubic meter 


cP . 


centipoise 


mg/min 


milligram per minute 


°F 


degree Fahrenheit 


min 


minute 


ft 


foot 


mj 


millijoule 


ft^/mln 


cubic foot per minute 


mL/min 


milliliter per minute 


ft/s 


foot per second 


yL/min 


microliter per minute 


g , 


gram 


mm 


millimeter 


g/cm^ 


gram per cubic 


urn 


micrometer (one millionth 




centimeter 




of a meter) 


gal 


gallon 


02 


ounce 


h 


hour 


pet 


percent 


hp 


horsepower 


psi 


pound per square inch 


in 


inch 


psla 


pound per square inch 


in/ in 


Inch per inch 




(absolute) 


keV 


thousand electron volt 


psig 


pound per square inch (gauge) 


L/min 


liter per minute 


s 


second 


lb 


pound 


yd3 


cubic yard 


lb/ft3 


pound per cubic foot 


ydVh 


cubic yard per hour 



Library of Congress Cataloging in Publication Data: 



Krantz, Gary W 

Selected pneumatic gunites for use in underground mining, 

(Bureau of Mines information circular ; 8984) 

Bibliography: p. 55-57. 

Supt. of Docs, no.: I 28.27:8984. 

1. Ground control (Mining). 2. Gunite. I. United States. Bureau 
of Mines. II. Title. III. Series: Information circular (United States. 
Bureau of Mines) ; 8984. 



'N295.U4 [TN288] 622s [622'. 2] 84-600137 



.i 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Background 4 

Acknowledgments 5 

Approach 5 

Gunlte fibers 9 

Gunlte additives and admixtures 11 

Silica fume 11 

Water reducers 12 

Accelerators 13 

Superplas ticizers 13 

Polymer latex additives 13 

Aggregate analysis 16 

Gunlte specimen collection 17 

Rebound analysis 23 

Gunlte dust 27 

Scanning electron microprobe analysis of silica fume 31 

Compressive strength analysis 33 

Flexural strength analysis 35 

Porosity and permeability analyses 39 

Delivery hose static discharge 45 

Gunlte operation crew requirements 46 

Gunlte cost analysis 48 

Conclusions and recommendations 52 

References 55 

Appendix A. — Gunlte rebound data 58 

Appendix B. — Air sampler dust data 59 

Appendix C, — Gunlte pore volume, density, and porosity data 60 

Appendix D, — Permeability data 61 

Appendix E. — Cost data 63 

Appendix F. — Toughness index discussion 64 

ILLUSTRATIONS 

1 . Dry-mix rotary gun used to apply gunlte specimen 4 3 

2. Dry-mix double-hopper spray machine used to apply specimen 5 3 

3 . Dry-mix rotary gun used to apply specimens 9 and 10 3 

4. Wet-mix gunlte gun and mortar mixer used to apply specimens 1-3 4 

5 . Location of the Lake Lynn Laboratory 6 

6. Plan view of experimental mine workings showing gunlte demonstration panel 

location 7 

7. Geologic column of strata in vicinity of Lake Lynn Laboratory 8 

8 . Gunlte fiber examples 9 

9. Rotary gunlte gun used in polymer latex gunning 14 

10. Styrene-butadiene latex polymer delivery pump 14 

11. Polymer latex gunlte application 15 

12. Water ring blockage by partially hydrated portland cement and polymer 15 

13. Grain size accumulation curves for samples 1-3 18 

14. Grain size accumulation curves for samples 4 and 5 19 

15. Grain size accumulation curves for samples 6 and 7 20 

16. Grain size accumulation curves for samples 8 and 9 21 



n 



ILLUSTRATIONS—Continued 

Page 

17. Grain size accumulation curve for sample 10 22 

18. NX-size cores of four gunite specimens 22 

19. Wet-mix gunite sample acquisition for splitting tensile analysis 23 

20. Six-inch-diameter by 12-in-long cylinders of six different gunite products 23 

2 1 . Gunite rebound collected and ready for weighing 26 

22 . Angled roof gunning produces very high rebound 26 

23. Near-vertical wet-mix roof gunning gives low rebound 27 

24. Near-vertical dry-mix roof gunning with reduced pressure gives low rebound 27 

25 . Gunite dust monitoring equipment 28 

26 . Gunite dust from the gun-loading operation 29 

27. Gunite gun dust on mine floor caused by worn friction plate or wear pad... 29 

28. Scanning electron microscope microphotograph of portland cement and silica 

fume 31 

29. Scanning electron microscope microphotograph of silica fume 31 

30 . Electron probe microanalysis of portland cement 32 

31. Electron probe microanalysis of silica fume 32 

32. Tinius Olsen 120,000-lb testing machine used in gunite analysis 33 

33. Stainless steel rotating bearing block used in gunite core compressive 

strength analysis 34 

34. Gunite compressive strength plot showing rapid failure 35 

35. Gunite compressive strength plot showing gradual failure 35 

36. Diamond-tipped saw used to cut steel-f ibered gunite specimens 37 

37. Flexural strength curve of a steel-f ibered gunite sample 39 

38. Gunite core air evacuation system for porosity analysis 41 

39 . Gunite permeability analysis system diagram 42 

40. Gunite permeability analysis equipment 43 

41. Hassler tube and associated core permeability measuring apparatus 43 

42. Linear regression curve fit of porosity and permeability 45 

TABLES 

1 . Gunite fibers tested at BOM Experimental Mine 10 

2. Normal fiber mix rates and typical diameter sizes 11 

3 . Polymer latex gunite materials tested 14 

4. Sand-size fraction content in gunite 17 

5 . Gunite rebound percentages 25 

6. Gunite dust data 30 

7 . Element X-ray spectrum data for silica fume 32 

8. Element X-ray spectrum data for cement 32 

9. Compressive strengths of f ibered-gunite specimens 36 

10 . Flexural strength of f ibered-gunite specimens 38 

11. Gunite density and porosity 41 

12. Gunite mean permeability values 44 

1 3 . Gunite crew requirements 46 

14. Gunite shooting rate 47 

15. Portland cement price data 49 

16. Gunite fiber price data 49 

17. Wet-mix gunite admixture costs 49 

18. Cost estimate for prebagged, wet-mix, silica fume, steel-f ibered gunite...^ 51 

19. Prebagged gunite cost comparison 51 



SELECTED PNEUMATIC GUNITES FOR USE IN UNDERGROUND MINING: 
A COMPARATIVE ENGINEERING ANALYSIS 

By Gary W, Krantz ^ 



ABSTRACT 

Fibered, portland-cement-based gunite products were applied in the 
Bureau of Mines Lake Lynn Laboratory Experimental Mine using a variety 
of pneumatic guns and gunning crews. The demonstrated wet-mix (with 
silica fume), dry-mix, and surface bonding products were sampled by the 
Bureau and subjected to a suite of engineering analyses. Gunite flex- 
ural and compressive strength, rebound, permeability, porosity, dust 
loading, shooting rate, crew requirements, and cost factors were evalu- 
ated. Steel, fiberglass, or polypropylene fibers were contained in all 
but two of the gunites tested. Both Bureau and private testing labora- 
tory analyses are provided for some products. Electron probe micro- 
analysis and X-ray diffraction analysis were performed on the silica 
fume fraction of the wet-mix gunite to characterize the dust. Aggre- 
gate size fraction distribution analyses were performed to provide 
strength relationships. Results indicate that all of the commercially 
available fibered-gunite materials tested can provide beneficial seal- 
ant, spall prevention, or roof stability control attributes for under- 
ground mining environments when applied by an experienced crew using a 
well-maintained gun, in accordance with product manufacturers' recom- 
mendations and when used for the designated purpose. 

^Engineering geologist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



Shotcrete, or pneumatically sprayed 
concrete or mortar, originated in the 
early 1900' s. The name "gunite" (former- 
ly the registered trade-mark of the Al- 
lentown Pneumatic Gun Co.) was coined by 
the Cement Gun Co. Gunite or shotcrete 
is defined by the American Concrete In- 
stitute as mortar or concrete conveyed 
through a hose and pneumatically pro- 
jected at high velocity onto a surface 
il) .^ The force of the pneumatically 
propelled material impacting on the sur- 
face causes compaction of the gunite into 
the fine surface irregularities, giving 
good adhesion. Pneumatic gunning results 
in a dense, dry (low water-cement ratio) 
coating that is capable of supporting 
itself in vertical or horizontal (over- 
head) applications. Gunite has been re- 
ferred to by a variety of names, includ- 
ing spraycrete, pneumatically applied 
mortar or concrete, airblown mortar or 
concrete, gunned mortar or concrete, and 
shotcrete. 

Aggregate size is the criterion used 
here to distinguish between gunite and 
shotcrete. Although sprayed mortar has 
been used for more than 50 years, only 
recent innovations in pneumatic equip- 
ment have enabled the use of aggregate 
as large as 1 in (25.4 mm). In gener- 
al, the pneumatically applied material 
is called shotcrete if it contains ag- 
gregates larger than 5 mm and gunite if 
the largest aggregate is smaller than 5 
mm. The largest aggregate contained in 
any material tested during this re- 
search project passed through a No. 4 
sieve (4.75 mm). Therefore, for purposes 
of this discussion, the material is re- 
ferred to as gunite or fibered gunite. 



and compressive strength. The type and 
amount of improvement are dependent upon 
the amount of fibers and their type, 
size, strength, and configuration (2^). 

Fibered gunite has a wide variety of 
uses including but not limited to the 
following: 

o Packwalls in longwall mining 

o Mine roof and rib control and 
support 

o Rock tunnel linings 

o Mine roof and rib sealant 

o Mine shaft lining (hoist and vent 
shafts) 

o Mine shaft collar installation 

o Underground joint or fault stabili- 
zation in mines 

o Highwall and rock slope 
stabilization 

o Dam construction 

o High-strength protective concreting 
for foundations 

o Thin-shell dome construction 

o Fire protection applications 

o Bridge repair 

The Bureau's major interest in the mate- 
rial is its mining applications. 



The inclusion of fibers in gunite im- 
proves many of the desirable engineering 
properties of the product. These include 
ductility, toughness, flexural strength, 
impact resistance, fatigue resistance, 

^Underlined numbers in parentheses re- 
fer to items in the list of references 
preceding the appendixes. 



Gunite has two primary application 
techniques — wet mix and dry mix. With 
the dry mix, the ingredients are volume- 
or weight-batched and mixed dry or pre- 
bagged (mixed) . The dry material is nor- 
mally fed to a pneumatically operated gun 
which delivers a smooth, continuous flow 
of material through the delivery hose and 
to the nozzle. The nozzle is equipped 



with a manually operated water injection 
ring system that provides even distribu- 
tion and mixing of water with the dry in- 
gredients as they are propelled through 
the nozzle and onto the application sur- 
face. Dry-mix machines are categorized 
as either high velocity or low velocity, 
depending on the application pressure and 
nozzle size. Figures 1-3 show three of 
the dry mix gunite guns used in this in- 
vestigation. (A fourth dry-mix-type gun 
is shown in figure 9.) 

With wet mix, water is mixed with the 
dry constituents in a batch mixture by 
either weight or volume. Weight batch- 
ing of the gunite ingredients is nor- 
mally recommended. The batch is normally 
tested for slump, entrained air con- 
tent, and uniformity before delivery to 
the application equipment. The mixture 
is moved through the equipment deliv- 
ery hose by a pump or with compressed 
air and sprayed (with compressed air) 
through the nozzle. Efficient, positive- 
displacement-type wet-mix delivery equip- 
ment has been recently introduced to the 




FIGURE 2o " Dry-mix double=hopper spray ma= 
chine used to apply specimen 5. 





FIGURE L - Dry-mix rotary gun used to apply 
gunite specimen 4. 



FIGURE 3. - Dry-mix rotary gun used to apply 
specimens 9 and lOo 



market. With this equipment, the wet 
mixture is forced through the delivery 
hose by a piston pump or screw-feed pump 
to the nozzle, where a compressed air in- 
jector ring pneumatically discharges the 
mixture at high velocity onto the appli- 
cation surface. A screw-feed type of 
gunite pump was used for the wet-mix ap- 
plication portion of this research proj- 
ect. Figure 4 shows the wet-mix gunite 
equipment and mixer used in this investi- 
gation. Accelerator fluids are easily 
added at the nozzle in quantities depen- 
dent on the application surface. Plas- 
ticizers and superplasticizers are added 
at the mixer to improve the workabil- 
ity (pumpability) of the material while 
maintaining the low slump and low water- 
cement ratio required in high-strength 
material. 

Various types of gunite guns and nozzle 
assemblies are commercially available and 
were used during this research product. 
Gun and/or nozzle selection depends on 




FIGURE 4. = Wet-mix gunite gun and mortar 
mixer used to apply specimens 1-3. 

the nature of the gunite product to be 
used, desired engineering parameters of 
the final product, quantity of material 
to be applied, rate of application, oper- 
ating gun-nozzle distance, cost, and 
other factors. 



BACKGROUND 



As early as 1911, small-diameter metal 
shavings and slivers of steel were tested 
in concrete products (and patents were 
issued) for the purpose of providing 
structural reinforcement. In the late 
1950' s, the Portland Cement Association 
began conducting studies to determine 
the strength properties of steel-fiber- 
reinforced concrete and mortar. The 
first detailed and documented crack- 
arrest research on steel-f ibered concrete 
products was conducted in 1963-64 at 
Carnegie-Mellon University in Pittsburgh. 
Experimentation with steel-f ibered shot- 
crete and gunite was conducted in 1971 at 
the Battelle Memorial Institute. During 
the same year, the Bureau of Mines began 
conducting research on the use of steel- 
fibered shotcrete and gunite for use in 
underground mine roof and rib structural 
control O) . 

By 1973, the use of steel fibers in 
shotcrete and gunite had advanced to such 
a degree that they were employed by the 
U.S. Army Corps of Engineers in a tunnel 
at the Ririe Dam in Idaho. Much of the 



early work on fibered gunite was con- 
ducted using relatively high fiber load- 
ings (130 to 260 lb/yd ^) and using steel 
fibers of relatively small diameter 
(0.010 in) and relatively high aspect 
ratios (up to 100) (3^). Aspect ratio of 
the fibers refers to the fiber length 
divided by its diameter, or equivalent 
diameter in the case of nonround fibers. 
The concrete material used in much of the 
early research was actually a cement-sand 
mortar containing no coarse aggregate. 
The research was devoted primarily to 
determining the effect of fiber content, 
configuration, and aspect ratio on the 
engineering properties of the mortar or 
concrete, including tensile strength, 
flexural strength, creep, impact resist- 
ance, fatigue resistance, and durability. 
As research on steel-f ibered mortar and 
concrete progressed during the 1960's, 
there was a trend to the use of concretes 
in favor of mortars and to the use of 
larger diameter, smaller-aspect-ratio 
steel fibers. The change to the lower- 
aspect-ratio fibers was necessitated by 
the unacceptably low workability of 



mortars or concretes containing large 
amounts of high-aspect-ratio fibers. The 
shift from mortar to concrete was made 
due to the high application volumes of 
coarse aggregate materials O) . 

The list of materials used for fibers 
in gunite has now expanded to include 
plastic, natural materials, steel (up to 
2 pet by volume) , standard and alkaline- 
resistant (AR) fiberglass, polypropylene, 
nylon, and other materials. The search 
continues to find inexpensive, high- 
strength, nondeteriorating, easily ac- 
cessible fibers with good workability 



characteristics for use in general and 
specialty applications. Additionally, 
silica fume, fly ash, ground slag, poly- 
mers , and latex-based additives have been 
introduced into the pneumatically ap- 
plied, cement-based products to impart 
improved adhesion and engineering proper- 
ties and to upgrade the sealant, chemical 
attack, and freeze-thaw characteristics. 
Use of the specialty materials has ex- 
panded considerably in the past 5 years 
and should continue to capture new mar- 
kets in a diverse array of construction 
and mining applications. 



ACKNOWLEDGMENTS 



The research effort, product demonstra- 
tion, comparative analyses, and findings 
compiled in this report were made possi- 
ble by the participation and generosity 
of four major gunite product manufactur- 
ing companies: B Bond Industries, Inc., 
Latrobe, PA; Burrell Construction and 
Supply Co., New Kensington, PA; Coal In- 
dustry Services Co., Pounding Mill, VA; 
and Elborg Technology Co., Pittsburgh PA. 
The author would also like to acknowledge 



the Mine Safety and Health Administration 
at Bruceton, PA, and the Department of 
Energy at Bartlesville, OK, who provided 
facilities and research testing equipment 
for portions of the investigation. The 
author is particularly indebted to the 
staff and management of the Bureau of 
Mines Lake Lynn Laboratory facility, who 
provided physical, logistical, and tech- 
nical assistance throughout the work. 



APPROACH 



The Bureau has been involved with 
f ibered-gunite development (for mining 
applications) since the early 1970' s. 
The Bureau's general philosophy regarding 
the material and the Bureau research lit- 
erature published to date on the topic 
support a generalized theory that the 
various fibered, portland-cement-based 
gunite materials can improve mine roof 
and rib stability and contribute to a 
safer underground mining environment when 
properly applied. Past Bureau research 
at the Spokane Mining Research Center 
(1975) recognized fibered gunite as a new 
and promising structural material for 
ground support ( 4_) . Recent domestic, 
f ibered-gunite product improvements have 
made inroads on the problems encountered 
in the early fibered-gunite research — 
mainly fiber balling (birds' nesting), 
lack of product homogeneity, fiber- 
aspect-ratio-caused handling problems , 
and high rebound or wastage. The advent 



of prebagged mixes has essentially re- 
solved the first three problems. Im- 
proved gunning equipment has reduced the 
latter problem considerably. A basic, 
unbiased research effort designed to com- 
pare several of the various fibered- 
gunite materials was needed in order to 
identify the properties of a cross sec- 
tion of the generic products that might 
be used at the Lake Lynn Laboratory. 

A research program .was designed that 
would allow wet-mix and dry-mix fibered- 
gunite material comparisons for the fol- 
lowing parameters: 

o Ease of gun loading 

o Gun-caused dust loadings 

o Gun noise and operation 

o Application ease 



o Rebound or wastage 

o Down-drift dust (cumulative) loading 

o Comparative engineering parameters:. 

Splitting tensile strength 
(Brazilian) 

Flexural strength 

Compressive strength 

Porosity 

Permeability 

o Comparative product mechanical sieve 
analysis 

o Product cost comparisons 

o Long-term durability (not reported 
herein) 

o Bonding strength (not reported 
herein) 

Owing to the vast number of gunlte fi- 
ber types, sizes, and configurations, the 
varying component mixture ratios (speci- 
fications), and the variety of gunlte 
guns, nozzles, and mix methods available, 
a comparative gunlte product research 
project had to be approached carefully. 
This point became even more cogent when 
product confidentiality was considered. 

The Bureau elected to conduct the gun- 
lte comparative research at the Lake Lynn 
Laboratory Experimental Mine, approxi- 
mately 60 miles south of Pittsburgh, PA, 
on the Pennsylvania-West Virginia border 
(fig. 5). Figure 6 presents a plan view 
of the mine and identifies the gunlte 
application area. 

A 25-ft section of D drift in the Lake 
Lynn Laboratory Experimental Mine was 
used for each product on a separate 
schedule basis that would allow approxi- 
mately 1 week of application time per 
product if needed. The four participat- 
ing gunlte manufacturers were permitted 
to prepare the roofs and ribs of their 




©Pittsburgh 
^ Bruceton 



O Uniontown 



^ Lake L ynn Loborot ory 



l__PA 

WV 

O Morgantown 
FIGURE 5. - Location of the Lake Lynn Laboratory. 

respective drift sections in accordance 
with their particular product needs. In 
some Instances, loose rock was barred 
down and the fresh surface was air-blown 
and/or water-mist-fogged prior to gunlte 
application. Although roof or rib bolts 
and/or wire mesh would have improved the 
properties of some of the tested prod- 
ucts, they were disallowed for this par- 
ticular comparative research effort. 

The experimental mine drifts at the 
Lake Lynn Laboratory are developed in a 
section of the Wymps Gap Limestone, a 
formation comprised of Intercalated lime- 
stones and calcareous shales. The lime- 
stone is grey, crystalline, and fossilif- 
erous. A 1-ft-thlck dark grey, calcare- 
ous shale stringer occurs at the roof-rib 
Interface in the mine drift where the 
gunlte test applications were performed. 
The shale stringer is prone to spalling 
and provides a suitable test of the capa- 
bility of the gunlte products to seal, 
support , and protect the rock from mois- 
ture absorption and subsequent expansion 
and/or spalling. Figure 7 presents the 
geologic column of the Lake Lynn Labora- 
tory site. 

Future mine explosion research to be 
conducted in D drift will subject the ap- 
plied gunlte to rigorous conditions. The 
bonding strength and durability parame- 
ters can be analyzed at a future time. 



Gunite application panels 



Gas-mixing stub^k 
Explosion-proof bwlkhead-"^ 

Ventilation stub— 



Explosion-proof bulkhead—* 

Gas-mixing stub— 




FIGURE 6. - Plan view of experimental mine workings showing gunite demonstration panel location. 



The floor of the experimental mine is 
concrete, which permitted rebound mate- 
rial to be collected with shovels for 
weighing. 

Dust collection and monitoring were 
performed. Mine temperature and relative 
humidity were monitored , as were all oth- 
er visible factors regarding the gunite 
application. 

Gunite product samples were collected 
in 6-in-diam by 12-in-long containers for 
splitting tensile strength tests. Four- 
by four- by fourteen-inch samples were 
sprayed directly into plywood forms for 
the flexural strength tests. Additional 
flexural tests were performed on sawn 
beams. A 24-in-square metal container 
was shot with an 8- to 10-in-thick sample 
of the various gunite products for cor- 
ing. NX-sized (2.1-in) diamond-drilled 
cores were taken from these sample blocks 



to perform uniaxial unconfined compres- 
sive strength tests. Additional testing 
for compressive strength was performed 
using sawn cubes. The data tables indi- 
cate the configuration of the sample used 
in the respective test procedure. 

The fibered gunite samples were tested 
by the Bureau using a Tinius Olsen^ hy- 
draulic universal testing machine. The 
machine has a 120,000-lb maximum pressure 
capacity and is equipped with multiscale 
electronic load-indicating dials. The 
loading rate was controlled with the use 
of an auxiliary pacing disc. An elec- 
tronic deflectometer was used to measure 
specimen deflection under load and was 
coupled to an x-y graph plotter to obtain 
stress-strain curves for each specimen. 

^Reference to specific products does 
not imply endorsement by the Bureau of 
Mines. 




UPPER KITTANNING COAL 
MIDDLE KITTANNING COAL 

LOWER KITTANNING COAL 

KITTANNING SANDSTONE 
CLARION COAL 

BROOKVILLE COAL 

HOMEWOOD SANDSTONE 

MERCER COAL 
CONNOQUENE3SING SANDSTONE 

QUAKERTOWN COAL 
SHARON COAL 



LAKE LYNN HIGHWALL FACE 



ZITZISZ SHALE, EXTREMELY WEATHERED, FRACTURED 



!^ 



WYMPS GAP LIMESTONE 



(FORMELY GREENBRIER LIMESTONE) ■ 





^■■i l i ' 



I I I I I 



I • I • I • ' 'T 



DEER VALLEY LIMESTONE 




CX3 



a 



w 



XI 



BURGOON SANDSTONE 



:^->zV 



MURRYSVILLE SANDSTONE ' 




SHALE, RED. MEDIUM HARD, FISSILE 
SHALE, GREEN, SILTY, SANDY SEAMS 



rrrLLL-T SHALE, RED AND GREEN, MEDIUM HARD, FISSILE 



LIMESTONE, GRAY. HARD. MASSIVE 
SHALE, DARK GRAY. BADLY BROKEN 
SHALE. RED. MEDIUM HARD. FISSILE 
LIMESTONE. GRAY. HARD. MASSIVE 
SHALE, GREEN, INTERBEDDED V\//LIMESTONE 
LIMESTONE. GRAY. HARD. MASSIVE 

LIMESTONE. DARK GRAY, HARD, MASSIVE 



QUARRY FLOOR 



FIGURE 7. - Geologic column of strata in vicinity of Lake Lynn Laboratory. 



GUNITE FIBERS 



Many types of fibers are commercially 
available for use in gunite. The fibers 
of a particular composition come in vary- 
ing lengths and/or diameters. Some are 
collated with water-soluble glue into 
bundles of 10 to 30 fibers to facilitate 
handling and mixing O ) . Figure 8 shows 
examples of some types of fibers. The 
more common types of gunite fibers in- 
clude E-f iberglass, AR-f iberglass , steel 
(carbon and stainless), polypropylene, 
and nylon. Polyethylene, polyvinyl chlo- 
ride, and polytetraf luoroethylene fibers 
may have limited gunite applications due 
to their alkalai resistance. 



E-fiberglass fibers are not highly rec- 
ommended in fibered gunite unless pro- 
tected by some means from expansive re- 
actions and silica dissolution caused 
by alkaline attack (introduced by the 
Portland cement) (6^). Fiber deteriora- 
tion has been reported when unprotected 
E-fiberglass fibers were used in gunite 
(2^, 6) . The alkaline attack results from 
three major concrete and/or gunite alka- 
lis: calcium, sodium, and potassium 
hydroxide. Glasses are available that 
exhibit very low reactivity, both in re- 
duction from alkalinity and in silica 
dissolved (upon exposure to alkalis) (7). 






^ 



B 








FIGURE 8. - Gunite fiber examples. A, 1-in cold-drawn wire, X 63; B, 1-in cold-drawn wire, X 200; 
C, 2-in melt-extract carbon steel, X 63; D, 0.71-in slit sheet, enlarged end, X 63; E, 0.71=in slit 
sheet, enlarged end, X 200; F, 1-in slit sheet carbon steel, X 63; G, 1-in slit sheet carbon steel, 
X 200; H, 0.75°in Duform, cold-drawn, X 63; /, 0.75-in Duform, cold-drawn, X 200; J, l°in melt ex- 
tract, X 63; K, 3/4-inmelt extract, X 63; L, 3/4-inmelt extract, X 200; M, 1/2-in polypropylene, X 63; 
A', 1-in fiberglass, X 63; 0, 1-in steel, deformed, X 63; P, 1.5-in drawn wire, deformed, X 63; Q, 1/2- 
in drawn wire, X 63; R, 1/2-in drawn wire, X 200. 



10 



The E-fiberglass fibers are more connnonly 15 are 
used in plastic or polymer reinforcement. fibers. 



variations of slit-sheet steel 



The more suitable, high-zirconia AR- 
fiberglass fibers developed in the late 
1960's are more commonly used in fibrous, 
portland-cement-based gunite. Type I ce- 
ment is normally recommended and commonly 
used with fiberglass fibers for general 
use, owing to cost and other factors. 
Type II or III cement may be recommended 
with some fibers if moderate sulfate 
action is anticipated or if high early 
strength is required. Five types of 
fiberglass-fiber gunites or surface- 
bonding cements were tested during the 
research period. Table 1 presents the 
various types of gunite fibers used in 
this investigation, their length, and the 
type of cement used. 



2. Cold-drawn wire method — cold-drawn 
wire is chopped to specified lengths. 
The wire fibers may also be deformed, 
kinked, or twisted. Sample 7 is a varia- 
tion of this type of fiber. 

3. Melt-extraction method — a process 
whereby a rotating, cooled disc with 
indentations the size of the fiber is 
dipped (spinning) in the surface of a 
molten pool of high-quality metal. The 
fibers formed by this technique can be 
altered in length, shape, and configura- 
tion by altering the disc indentations. 
This fiber type was not tested; however, 
figure 8 shows variations of the fiber 
type. 



Steel fibers are manufactured by many 
different processes for use in fibered 
gunite, including — 

1. Slit-sheet method — a sheet of steel 
is cut or slitted, producing a square 
or rectangular fiber. The fibers may 
then be deformed at the ends, kinked, 
or twisted. Samples 1-3, 6, 10, 11, and 



The steel fibers range in strength from 
50,000 to 300,000 psi ultimate strength. 
Fiber sizes range from 1/2 by 0.010 in 
to 2-1/2 by 0.030 in (_2 ) . Fibers with 
kinks , deformed ends , or other locking 
mechanisms develop higher ultimate flex- 
ural and/or splitting tensile strength 
gunite owing to the increased fiber 
pullout resistance. Fibers with larger 



TABLE 1. - Gunite fibers tested at BOM Experimental Mine 



Sample 



Fiber type 



Length of 
fiber, mm 



Type of 
cement 



Type of 
mix 



1.. 

2., 

3., 

4., 

5I, 

6., 

7., 

8l, 

9., 

10., 

11.. 

12.. 

13.. 

14.. 

152, 

162, 

172, 



Steel (slit-sheet). 

. . .do 

. . .do 

AR-f iberglass 

...do 



Steel (slit-sheet)... 
Steel (cold-drawn),.. 

E-fiberglass 

AR-f iberglass 

Steel (slit-sheet)... 

. . .do 

No fiber 

Polypropylene 

AR-f iberglass 

Steel 

No fiber 

Polypropylene , 



18 

18 

18 

12.7 

12.7 

25.4 

30 

12.7 

12.7 

25.4 

25.4 

NAp 
25.4 
12.7 
25.4 

NAp 
25.4 



III 

III 

III 

II 

II 

lA 

lA 

III 

I 

I 

I 

I 

I 

I 

I 

I 

I 



Wet 
Wet 
Wet 
Dry 
Dry 
Dry 
Dry 
Dry 
Dry 
Dry 
Dry 
Dry 
Dry 
Dry 
Dry 
Dry 
Dry 



NAp Not applicable. 

^Samples 5 and 8 were surface-bonding mortars (cement), 

2samples 15-17 were shot with latex polymer. 



11 



surface area (square or rectangular as 
compared to round) have more concrete 
bonding area. Accordingly, fibers with 
a scarified (pitted) surface have a 
greater surface area than smooth-surfaced 
fibers. 

Corrosion of steel fibers in gunite 
with a high water-cement ratio may pose a 
deterioration problem. The free moisture 
in wet concrete (and gunite) provides an 
aqueous medium which facilitates trans- 
port of soluble chemical substances, such 
as oxygen, calcium hydroxide, alkalis, 
and chlorides, toward the metal. It also 
increases the electrical conductivity of 
the material, thus aiding any tendency 
for electrochemical corrosion (7^) . For 
this reason, high-quality steel or stain- 
less steel is used by many fiber manufac- 
turers in an effort to prevent or at 
least reduce corrosion. 

Polypropylene fibers are essentially a 
crystalline thermoplastic produced by 



polymerizing polypropylene monomer in the 
presence of a catalyst. The fibers are 
chemically inert, are noncorrosive, and 
have a high chemical resistance to min- 
eral acids, bases, and inorganic salts. 
The fibers are recommended for use as a 
secondary type of reinforcement in con- 
crete (maintains integrity of concrete 
against cracking) rather than for primary 
reinforcement (structural support). In 
gunite the polypropylene fibers arrest 
the cracking process during the plastic 
shrinkage stage, creating microcracks 
rather than large cracks (8^) . The poly- 
propylene fiber tested in this research 
effort is manufactured in a fibrillated 
bundle which springs open during mixing. 

A generalized mixing rate for the vari- 
ous fiber types is presented in table 2. 
A range of mix rates is provided, depend- 
ing on manufacturers' specifications and 
the strength or specialty requirements of 
the gunite. 



GUNITE ADDITIVES AND ADMIXTURES 



Some gunite manufacturers, particularly 
wet-mix gunite manufacturers, have re- 
cently introduced a variety of additives 
and admixtures into gunite to improve 
strength, adhesiveness, cohesiveness , and 
freeze-thaw and abrasion-resistance char- 
acteristics, and to reduce rebound. Six 
of the gunite products tested in this 
investigation included known additives 
or admixtures. A brief discussion is 
provided of the major additives and 



tures used in the wet-mix gunite in this 
investigation. 

SILICA FUME 

Silica fume and ferrosilicon dust (es- 
sentially the same material but with 
slightly different chemical compositions) 
are essentially by-products of silicon 
metal and ferrosilicon alloy manufactur- 
ing. The light grey to grey silica fume 



TABLE 2. - Normal fiber mix rates and typical 
diameter sizes ^ 



Fiber type 



pet (by vol) 



lb/yd; 



Typical diam, in 



Fiberglass: 

E type 

AR type 

Steel 

Polypropylene. . 



1 -5 

1 -5 

.4-2 



.1 



40 
40 
50-265 
1.6 (av.) 



0.0002 to 0.0006 

0.010 to 0.030 
0.0008 to 0.015 



^These figures represent the concentration of fibers 
normally used in gunite products. The figures do not im- 
ply that equivalent performance will be achieved by the 
various fiber types at these concentrations. 



12 



develops above the molten burden in an 
electric arc furnace as escaping SiO gas 
oxidizes and condenses into a solid vi- 
treous particulate Si02 form (9^) , The 
initial investigations on the effect of 
silica fume in concrete were conducted in 
the 1950' s (10) . The developmental work 
and actual use of the material started in 
1969 (U), 

Silica fume production in the United 
States and Canada is difficult to esti- 
mate since it is directly tied to the 
currently depressed ferroalloys industry, 
but 500,000 tons per year of silica fume 
are reportedly available in the Western 
World and Japan. Total annual production 
from the United States and Canada is ap- 
proximately 205,000 tons of silica fume 
with Si02 content higher than 70 pet. Of 
this, only 80,000 to 120,000 tons is ex- 
pected to be of suitable quality for con- 
crete (and gunite) use. Silica fume from 
15 sources in the United States and Can- 
ada had 63.3 to 96 pet Si02 , 0.10 to 5.45 
pet AI2O3, 0.10 to 12.2 pet Fe203, and 
1.75 to 10 pet C (11). The silica fume 
tested in this investigation was found by 
the Bureau to have the above components 
plus trace amounts of sulfur, potassium, 
calcium, titanium, and chromium. Silica 
fume size (diameter) was determined to be 
0.5 to 1 ym in the Bureau scanning elec- 
tron microscope. 

Cost of the silica fume varies consid- 
erably. Although it was once discarded 
as an unwanted byproduct , research and 
testing have turned it into a marketable 
commodity ranging in price from $50/ton 
to $75/ ton (bulk) at the plant. Expecta- 
tions are that a price of $100/ ton may 
be reasonable in the future. Silica fume 
is available from a variety of sources 
across the United States. 

Silica fume is difficult to handle, 
store, and transport owing to its ex- 
tremely small particle size. Its bulk 
density is very low at 12 to 20 Ib/ft^ 
(12) . Caution had to be exercised in 
handling the material in the drafty mine 
environment at Lake Lynn. Silica fume is 
highly pozzolanie and can be used to some 



extent in most applications as a cement 
replacement. The material is hard to 
disperse in wet-mix gunite and consumes 
considerable water. The specific area of 
condensed silica fume is very high (up to 
20,000 m^/kg compared to 600 m^/kg for 
cement) (13) . Water reducers and/or su- 
perplasticizers are used with silica fume 
to control the workability and pumpabil- 
ity of the mix. Mixing silica fume with 
water as a slurry is a convenient way of 
handling the material in bulk volume. 
Reportedly 1 ton of water is mixed with 1 
ton of the silica fume (13) . Superplas- 
ticizer is frequently added to maintain 
dispersion of the silica fume in the wa- 
ter. The slurry can then be conveniently 
added to the concrete or wet-mix gunite. 

The use of silica fume in the wet-mix 
gunite required the contained sand-sized 
aggregate to have a specific fine aggre- 
gate size fraction distribution. One 
bulk volume of purchased sand was re- 
jected by the wet-mix manufacturer when 
lower-than-expected ultimate strengths 
were discovered owing to an unacceptable 
size fraction distribution. 

The increased cohesiveness of the wet- 
mix gunite with silica fume allowed a 
thickness of more than 2-1/2 to 3 in to 
be placed on the mine roof without sag- 
ging or slumping. The fine silica fume 
material contained in the wet mix tended 
to give a smooth overall finish to the 
gunite. Even the protruding steel fibers 
appeared to have a paste coating on them. 
The coating tended to prevent serious 
puncture wounds and also added to the 
strength of the material. 

WATER REDUCERS 

Water reducers, mainly of the lignosul- 
fonate or hydroxylated carboxylic acid 
type, are used to improve gunite (wet- 
mix) workability and cohesiveness in the 
plastic state. Once hardened, the mate- 
rial adds to the product strength while 
reducing permeability and increasing dur- 
ability. When added to a wet-mix gunite 
(or concrete) , the water reducer can give 
a significant increase in slump with the 



13 



same water-cement ratio, or the water- 
cement ratio can be reduced to achieve 
the same slump as for a mix not con- 
taining the water reducer. (The reduced 
water-cement ratio relates to a direct 
increase in strength. ) The higher slump 
adds to an increased workability or, in 
the case of wet-mix gunite, an increased 
pumpability. The wet-mix gunite tested 
in this investigation had a slump ranging 
from 3-1/2 to 5 in. 

ACCELERATORS 

Gunite accelerators are used to shorten 
product set time, thereby reducing any 
sagging or sloughing tendencies when 
thick applications are to be made in 
a single pass. The accelerators can 
improve workability and increase final 
product strength. Although some 
chloride-containing accelerators are 
known to reduce the ultimate gunite 
strength, nonchloride accelerators are 
available. 

SUPERPLASTICIZERS 

Superplasticizers are chemically dis- 
tinct from normal plasticizers or water 
reducers. They are better known as high- 
range water reducers since they can be 
used at high dosage levels without the 
problems of set retardation or excessive 
air entrainment associated with high 
rates of addition of conventional plasti- 
cizers or water reducers (14) . The su- 
perplasticizers are grouped into several 
chemical categories, including the sulfo- 
nated melamine formaldehyde condensates, 
sulfonated naphthalene formaldehyde con- 
densates, and modified lignosulf onates 
(15) . These chemicals are essentially 
salts of organic sulfonates. Their names 
are conveniently shortened to type M 
(melamine) , type N (naphthalene) , and 
type L (lignosulf onate) . Type M forms a 
lubricating film on the particle sur- 
faces, type N electrically charges the 
particles and they repel each other, and 
type L decreases the water surface ten- 
sion. When well dispersed, the cement 
particles not only flow around each other 
more easily but also coat the aggregate 



more completely. The result is a con- 
crete that is both stronger and more 
workable ( 16 ) . The investigated wet-mix 
gunites containing the superplasticizer 
took on a silky, almost lustrous feel and 
could have been pumped for great dis- 
tances without clogging the placement 
and/or delivery hoses. The superplasti- 
cizers' effect of dispersing "fines" 
makes them perfect and needed admixtures 
for gunite (wet-mix) containing silica 
fume. 

The gunite slump increase achieved by 
adding conventional superplasticizers is 
time and temperature dependent and can be 
completely lost within 60 to 90 min after 
mixing. Although higher dose rates can 
slow the rate of slump loss, too much 
superplasticizer results in a total loss 
of cohesiveness and the initiation of 
mix segration, a condition known as to- 
tal collapse (16) . One such incident oc- 
curred at the Lake Lynn Laboratory Mine 
during the batching of the wet-mix gun- 
ite. The sensitive balance of the silica 
fume-water reducer-superplasticizer was 
overexceeded in one batch, and the mix 
had to be discarded and cleaned out of 
the gunite pump system. The introduction 
of a variety of specialty additives and 
admixtures into wet-mix gunite, there- 
fore, should only be attempted by a high- 
ly trained specialist. Since many of the 
admixtures are liquid, they cannot all be 
conveniently measured and prebagged in 
dry form at this time. 

POLYMER LATEX ADDITIVES 

Polymer latex additives have been used 
in portland-cement-based products to im- 
part special desired properties, includ- 
ing adhesion improvement, permeability 
reduction, resistance to chloride attack, 
freeze-thaw deterioriation prevention, 
impact resistance, reinforcement steel 
protection, and strength improvement. 
Owing to the prospective use of the addi- 
tive in fibered gunite for mining pur- 
poses, a test gunite demonstration was 
arranged between one dry-mix gunite manu- 
facturer and a polymer latex producer. 



14 



The polymer latex used in the test ap- 
plication (at the gunite manufacturer's 
facilities) was a styrene-butadiene poly- 
meric emulsion in which the polymer com- 
prises 47±1 pet by weight and water makes 
up the balance (53 pet). The polymer 
contained 64±2 pet styrene and 36±2 pet 
butadiene. Mean polymer particle size 
was reported to be 2,034±300 A. The 
polymer weighed 8.4 lb/gal. 

The polymer latex gunite test was con- 
ducted at the facilities of one of the 
participating gunite manufacturers. Test 
panels of a variety of fibered gunite 
materials were shot. Table 3 lists test 
panel shots and provides sample number 
identification for the various products. 
The gunite manufacturer's gunning crew 
had no prior experience with polymer la- 
tex and, therefore, relied solely on the 
polymer manufacturer's representative for 
guidance in mix-ratio proportioning. 

The various prebagged gunite products 
demonstrated during this phase of the 
work were shot using the rotary gun shown 
in figure 9. Sample blocks 15-17 were 
shot with the polymer latex using a 
gasoline-powered pump to deliver the 
latex to the nozzle directly from a 55- 
gal drum. The delivery system is shown 



TABLE 3. - Polymer latex gunite 
materials tested 



Sample 



Material 



11 Steel fiber. 

12 Sanded gunite , no fiber . 

13 Polypropylene fiber . 

14 AR-f iberglass (1 pct).^ 

15 Steel fiber with polymer 

latex. 

16 Sanded gunite, no fiber, 

polymer latex. 

17 Polypropylene fiber with 

polymer latex. 

^Prebagged, fibered or nonfibered mixes 
were gunned into test panels with and 
without polymer latex. 

^Polymer latex was not tested in a 
fiberglass-fibered gunite. 

in figure 10. Figure 11 shows the gun- 
ning operation in progress. Antifoaming 
agents were not employed , and flow cones 
were not used to determine workability. 

Considerable difficulty was experienced 
in obtaining a consistent latex-gunite 
flow from the nozzle. The polymer latex 
caused partial blockage of the nozzle wa- 
ter ring assembly (fig. 12) by partially 
hydrating the cement fraction and forming 




FIGURE 9. - Rotary gunite gun used in polymer 
latex gunning. 





FIGURE 10. - Styrene-butadiene latex polymer 
delivery pump. 



15 




FIGURE 11,- Polymer latex gunite application. 




FIGURE 12, " Water ring blockage by partially hy- 
drated portlond cement and polymer. 



a sticky residue within the orifices. An 
attempt was made to correct the situation 
by drilling the orifices larger (+1/32 
in) and increasing the latex polymer de- 
livery pressure. The alterations par- 
tially corrected the problem, and hydra- 
tion of the dry-mix gunite appeared to be 
adequate; however, the gunned material 
had a very high slump and would not have 
been suitable for application on a verti- 
cal surface. The use of a longer hose 
extension between the water nozzle body 
water ring and the nozzle tip along with 
higher latex polymer pump pressure and 
lower volume would have provided a longer 
wetting chamber, hence more thorough hy- 
dration of the gunite by the latex poly- 
mer. With the equipment setup used, how- 
ever, an excess of polymer was required 
to hydrate the dry mix in the short 
water-ring-to-nozzle-tip distance. This 
overabundance of latex polymer, plus the 
variation of feed rate caused by air 
compressor flow variation and subsequent 
gun speed changes , gave less than opti- 
mum test shot specimens for analysis. 
The polymer specimens were seriously 
laminated. 

Tables 9 (p. 36) and 10 (p. 38) include 
the comparative compressive and flexural 
strengths for the seven products demon- 
strated during the latex polymer tests 
(samples 11-17) and presented in table 3. 
The engineering properties were deter- 
mined by Froehling and Robertson, Inc., 



laboratories. Twenty-eight-day compres- 
sive and flexural strength decreases (36 
to 49 pet and 24 to 29 pet, respectively, 
compared to nonpolymer steel and poly- 
propylene specimens) were observed for 
the steel- and polypropylene-fibered sam- 
ples shot with the latex product (samples 
15 and 17, respectively) owing to the 
gunite mix hydration problems . The non- 
fibered, sanded gunite with latex (sample 
16) gave better results; however, this 
was not due to the absence of fibers. 
The equipment and gunning conditions were 
optimum at the time this material was 
gunned. The 28-day compressive strength 
of the sanded gunite-latex polymer sample 
(16) was only 90 pet of the nonpolymer 
strength, but the sample showed a sig- 
nificant increase in flexural 28-day 
strength (173 pet of nonpolymer materi- 
al) . The nonf ibered polymer specimen 
(sample 16) had the best hydration char- 
acteristics of the series. In general, 
the compressive-flexural characteristics 
of the three gunite-polymer materials are 
considered to be less than those achiev- 
able with the proper gunite-latex deliv- 
ery equipment. 

The permeability reduction achieved by 
the polymer latex in specimens 15-17 
compared to that with nonpolymer speci- 
mens was impressive. Although each spec- 
imen tested contained lamination zones 
(hence the poor compressive and flexural 
strengths), the permeabilities were less 



16 



than the accurate measurable lower limit 
of the research apparatus (1 >^ 10~^ dar- 
cy). Permeability analyses are discussed 
in more detail later in this report. The 
permeability reduction obtained by the 
use of a polymer latex additive should 
impart beneficial freeze-thaw character- 
istics and rebound percentage reduction; 
however, the high cost of the material 



could preclude its use in general appli- 
cations. The material has excellent po- 
tential for use in specialty (reduced 
permeability) gunite applications in deep 
mines such as high water intake zones , 
where high sulfur or sulfate may be en- 
countered, or where the gunite may be 
exposed to large volumes of cold, moist 
air, such as at or near shaft collars. 



AGGREGATE ANALYSIS 



Elandom samples of the tested prebagged 
dry gunite products and of the sand- 
sized fraction of the wet-mix were sub- 
jected to mechanical sieving analysis. 
The dry sieve samples were taken directly 
from freshly opened bags. Multiple sam- 
ple splitting was not performed owing to 
the prospective high loss of the cement- 
sized fraction and to the fibers. One- 
thousand-gram random samples of each 
product were placed in a stacked series 
of screen sieves containing 4-, 10-, 20-, 
40-, 100- , and 200-mesh screen (4.76, 
2.0, 0.84, 0.42, 0.149, and 0.074 mm re- 
spectively) plus the bottom pan. The 
stacked sieve screens were covered with a 
top section and placed in a RO-TAP shaker 
for 10 min. The retained content of each 
sieve was weighed, and a sample was col- 
lected for microscopic analysis. Only 
one random sample from one premixed bag 
of dry -mix gunite was tested. The sample 
analysis, therefore, may or may not be 
totally representative of the product. 

The steel-f ibered samples were sub- 
jected to magnetic fiber separation. 
Samples containing fiberglass fibers were 
hand-picked of their fiber content. The 
magnetic technique resulted in the col- 
lection of 100 pet of the steel fibers. 
The hand-picking procedure was only cap- 
able of recovering 90 to 95 pet (esti- 
mated) of the fiberglass fibers. The fi- 
ber weight (and volume) percentages may, 
therefore, differ from the manufacturer's 
specifications. The sand-sized (10- to 
200-mesh) fraction of the various gunite 
products was analyzed for differences in 
grain shape, nominal size, and size frac- 
tion distribution. 

The grain shape (roundness and spheri- 
city) of the sand-sized materials had a 



decisive effect upon the grain size col- 
lected by the respective sieves. The 
parameter also relates to gunite strength 
properties. Grain fractions with three 
equidimensional (nearly spherical) axes 
(a=b=c) perpendicular to each other ex- 
hibited size separation reflecting the 
diameter characteristics of the grain. 
Grain fractions with multidimensional 
(elongate) axes (e.g., a=b^c or a^b^c) 
exhibited size fraction separation depen- 
dent primarily on the minor axis dimen- 
sion. Some size fraction percentages, 
therefore, may be slightly distorted. 

The roundness classification of the 
material is an empirical analysis which 
can be described qualitatively as follows 
(17): 

1. Angular - all corners sharp, having 
radius of curvature equal to zero; sur- 
face not abraded. 

2. Subangulav - corners not sharp but 
having very small radius of curvature; 
most of surface not abraded. 

3. Suhvounded - corners very notice- 
ably rounded but surface not completely 
abraded. 

4. Rounded - entire surface abraded; 
radius of curvature of sharpest edges is 
about equal to radius of maximum in- 
scribed circle. 

As seen in two dimensions, either in 
sawn cores or cubes , the sand and aggre- 
gate grains were either equidimensional 
or elongate. Roundness of the aggregate 
is very important owing to the interlock- 
ing nature of the grains in the hardened 
product. 



17 



Sand-sized fraction (10- to 200-mesh) 
analysis was critically important since a 
major proportion of the material from the 
samples tested (up to 97 pet) falls with- 
in the size fraction category. Table 4 
presents the percentage composition of 
the sand-sized fraction of each sample 
product tested. Figures 13 through 17 
show the grain size accumulation curves 
for the various gunites. Although the 
sand-sized fraction appears to be quite 
high for some products, the percentages 
are somewhat misleading. The cement par- 
ticles tended to agglomerate into small 
round balls during screening and were re- 
tained, in various proportions, on the 
100- and 200-mesh screens. 

TABLE 4. - Sand-size fraction (10- to 
200-mesh) content in gunite 



Sample 


10 to 


200 mesh. 


10 to 100 mesh. 




pet 


(by wt) 


pet (by wt) 


1-3... 


1 


100 


95.16 


4 




88.53 


68.67 


52.... 




67.05 


25.96 


6 




79.20 


76.28 


7 




93.33 


73.45 


82.... 




91.14 


69.44 


9 




86.98 


69.43 


10 




97.32 


87.81 



'^Raw sand tested. 



'^Samples 5 
cements. 



and 8 are surface-bonding 



The characteristics of the sand-sized 
aggregate have a direct bearing on the 



ultimate engineering properties of the 
final gunite product. The influence of 
aggregate grading and shape on the prop- 
erties of concrete has been studied since 
the invention of portland cement, and 
many methods have been proposed for ar- 
riving at an "ideal" grading. None, how- 
ever, has been universally acceptable 
(18) . In concrete, the coarser fractions 
of aggregate cause bleeding and segrega- 
tion while at the same time increasing 
strength and reducing shrinkage, crack- 
ing, and cost. The fine fraction (alone) 
reduces workability unless high water- 
cement ratios are used. In gunite, the 
fine and intermediate fractions are re- 
quired to fill in the matrix and contrib- 
ute to the final product density. In 
general, portland-cement-based products 
take on the hardness and abrasion resist- 
ance characteristics of the aggregate. 

Although the pneumatically applied gun- 
ite may have exhibited size-fraction- 
induced rebound or slump characteristics 
in this research, the major affected fac- 
tors were the ultimate product engineer- 
ing properties. Since each company pro- 
vided its own application equipment and 
nozzle operators for the test demonstra- 
tions , the application variables were too 
numerous to permit a more detailed evalu- 
ation of the aggregate characteristics' 
influence on the final product engineer- 
ing properties. 



GUNITE SPECIMEN COLLECTION 



The most serious obstacle in the re- 
search effort was obtaining high-quality 
test specimens of the fibered gunite ma- 
terial that were representative of the 
applied product. Samples of the gunite 
were carefully prepared and collected 
and were left in the damp, moist mine 
environment covered in plastic for 24 h 
before being moved. The samples were 
then moved, moistened, and covered to 
protect them from rapid moisture loss 
until testing. 

Core drilling of the 24- by 24-in test 
panels for compression test specimens 



revealed that all of the steel-fibered 
products of the dry-mix type contained 
sandy, laminated zones up to 1/2 in 
thick. The laminated zones were randomly 
dispersed throughout the 7- to 9-in-thick 
sample; therefore, they are not the re- 
sult of side or bottom rebound aberra- 
tions. Figure 18 shows (on the right) 
three different dry-mix product cores 
that contain laminations . The specimen 
on the left is one of the wet-mix gunite 
products , which contain silica fume and 
additives. All four samples were rolled 
on a damp sponge to show the preferential 
water absorption of the lamination zones. 



18 



r 










MECHANICAL ANALYSIS GRAIN SIZE ACCUMULATION CURVE 






2" 
11/2" 

1" 
3/4" 

1/2" 

3/8" 
1/4" 

hit 


Sieve Sizes - U.S. Standard 


100 




I III 


' 




^, 


1 
1 




I ' 1 
1 1 1 


i-- 


1 ' 1 


I'll 




10 










\, 


1 




1 1 1 
1 1 1 


/ 










90 










N 


1 

VI 




1 1 1 
1 1 1 


/ 










20 












y^ 




y 












80 












■■HMU. : 1/ 












30 












1 
1 


1 
1 


T--J/ 












70 












1 




T 












T3 

c 40 

10 












1 
1 




1 1 1 












60 1 
<n 












1 
















0) 

t 50 












1 
















50 t 

c 












1 
















a> 
2 60 

<?: 

70 












1 
















An " 




SAMPLE 1-3 

SAND FRACTIOI 

ONLY 

' II 1 


L 






1 
















40 5; 


1 






1 
















30 


1 






1 
















80 


yi 1— 






1 
1 
















20 


1 






1 
















90 


1 






1 
1 
















10 


1 






1 
















100 




> 1 1 M 1 






1 


1 








1 1 1 


1 1 1 1 


1 1 1 




-d dP °§§g 
Particle Size Diameter in Millimeters , 




Coarse Aggregate 


Coarse Sand 


Fine Sand 


Silt 


Clay 





c 

T 

c 







MECHANICAL ANALYSIS GRAIN SIZE ACCUMULATION CURVE 






2" 
1 1/2" 

1" 
3/4" 

1/2" 

3/8" 
1/4" 


Sieve Sizes - U.S. Standard 

o o o 
r 00° ^cMc5-» <B y- cge\j 


100 




1 III 


1 




V 


1 


1 
1 




1 1 
1 1 


/^- 


1 1 


'III 




10 










\ 


1 
1 


1 




[^ 












90 










\ 


1 
1 


1 




>l 












20 










\ 


1 
1 


1 
1 




y 












80 












u 


1 

1 


g 


r^\ 












30 












i 


1 

1 > 


* 














70 












1 


-^ 




























1 


T 
1 
















60 1 
in 


c 40 












1 


1 
1 
















0) 

^ 50 












1 


1 
















50 t 

c 












1 


1 
1 














1 1 1 


2 60 












1 


1 














1 1 1 


An " 


- 


SAMPLE 1-3 
REJECT SAND 

1 III 


1 






1 


1 
















40 oj 
a. 


70 


1 






1 


1 
















30 


1 
1 






1 


1 
















80 


1 






1 


1 
















20 


1 






1 


1 
















90 


1 






1 


1 
















10 


1 
_ . 1 






1 


1 
1 
















100 




1 : 1 1 II 1 






1 


1 




1 1 






1 L 


1 1 1 J 




. 

3 


"" - -o dp pggc 

Particle Size Diameter in Millimeters 




Coarse Aggregate 


Coarse Sand 


Fine Sand 


Silt 


Clay 





FIGURE 13. - Grain size accumulation curves for samples 1-3. 



19 









MECHANICAL ANALYSIS GRAIN SIZE ACCUMULATION CURVE 






2" 
1 1/2" 

1" 
3/4" 

1/2" 

3/8" 
1/4" 


Sieve Sizes - U.S. Standard 


inf) 









1 




\, 


1 


T 
1 




1 




I ' 1 
1 1 1 


'111 


1 1 1 










] 




\ 




1 






1 




L^l ! 






90 


10 










\ 




1 

1 






r , 1 
.4 11 1 






20 












w_ 


1 




>U^' 


' 1 1 






no 














-9^ 

1 




1 












30 














1 

1 




1 










70 














1 




1 












T3 














1 
1 




1 










O) 

60 i 

CO 


c 40 














1 




1 










CC 50 




























50 °- 














1 








1 1 1 






c 


<s> 














1 














o 

40 £ 

Q. 


Sf 60 

0) 


— 




1 








1 














0. 


SAMPLE 4 


1 — 1 
1 








1 


1 1 1 












30 


70 


1 — ' 
1 








1 


1 1 1 
















1 — ' 
1 








1 














?n 


80 


1 — ' 
1 








1 


















1 — ' 
I 








1 
1 














10 


90 


1 — 

1 








1 

.— 1 




— 1 














II 1 1 1 1 








1 










1 1 1 1 




. 


100 


>" '- -d oP °8pc 

Particle Size Diameter in Millimeters 




Coarse Aggregate 


Coarse Sand 


Fine Sand 


Silt 


Clay 





c 

c 







MECHANICAL ANALYSIS GRAIN SIZE ACCUMULATION CURVE 






2" 
1 1/2" 

1" 
3/4" 

1/2" 

3/8" 

1/4" 


Sieve Sizes - U.S. Standard 

-, <OOQOQ o pt^ 

r 00? ^ c^ ^^ (S i= SfM 
1 j^ ^ — 


100 






1 










1\ 






1 ' 1 


■ III 


1 1 1 


10 




1 III 












\ 












90 
















\ 












20 
















\ 


\ 




1 1 1 






80 
















^ 






V\ 






30 
















^ 






/ 1 






70 
















\ 




f 








•o 

2 .in 


















\ 


/ 








60 I 
in 


c 40 


















>J 


» 








^ 50 




























50 t 

c 














] 














e 60 




























o 
40 5 




SAMPLE 5 


1 






















70 


1 






















30 


1 
1 






















80 


1 






















20 


1 






















90 


\_ 


















II 1 1 




10 


1 






















100 




.1 1 M 1 






1 










1 1 1 


lJ_J_i 


1 1 1 


. 
I 


Particle Size Diameter in Millimeters 




Coarse Aggregate 


Coarse Sand 


Fine Sand 


Silt 


Clay 





FIGURE 14. - Grain size accumulation curves for samples 4 and 5. 



20 



c 







MECHANICAL ANALYSIS GRAIN SIZE ACCUMULATION CURVE 






2" 
1 1/2" 

1" ■ 
3/4" 

1/2" 

3/8" 
1/4" 


Sieve Sizes - U.S. Standard 
_, tooooQ o or>- 


100 




T Til 


T 






Tv. 


1 


1 ' ' 


^ 


1 i 1 


''If 


1 1 1 


10 












1 \ 






7 










90 












\ 






{ 


\ 








20 












' 


V 


1 1 1 ^ 




\ 








80 














1 ■ 


■^1 / 












30 
















Tl^^^ 


— 1 










70 
















1 1 T 


1 










■D 




























60 1 


c 40 




























rr 






















1 1 






50 i 

c 


°- 50 




























9> 

2 60 




























u 

40 5 

Q. 


— 


SAMPLE 6 


1 






















70 


1 






















30 


1 
1 
















1 1 1 






80 


1 


















1 1 1 1 




20 


1 
1 


















II 1 1 
1 1 1 1 




90 


1 


















1 1 II 
1 1 1 1 




10 


1 

_1 


















1 1 1 1 
1 1 1 1 


1 1 1 


100 




II 1 1 1 1 
















1 1 1 


1 1 1 1 


1 1 1 


. 

3 


" - -o dp c=goc 

Particle Size Diameter in Millimeters 




Coarse Aggregate 


Coarse Sand 


Fine Sand 


Silt 


Clay 





r 

r 
C 








MECHANICAL ANALYSIS GRAIN SIZE ACCUMULATION CURVE 






2" 
1 1/2" 

1" 
3/4" 

1/2" 

3/8" 
1/4" 


Sieve Sizes ■ U.S. Standard 


100 




T 111 






"■^i 


k 


1 




1 1 


1 


1 i 1 


'III 


1 1 1 


10 












\ 


1 






1 / 
1 / 








90 












\ 


1 






1 / 








20 












1 \ 


1 

\ 


-1 


' 










80 
















\ , 


4 


^ L — -w- 


1 








30 














1 














70 














1 
1 










III 




T3 

c 40 




1 1 1 1 










1 
1 














60 i 

C/) 














1 
1 














^ 50 














1 






1 








(0 

50 t 

c 














1 

1 






1 








ID 

if 60 
70 














1 














u 

40 S 

a. 




SAMPLE 7 
1 III 


1 








1 














1 








1 














30 


1 
1 






1 


1 














80 


1 
1 






1 


1 














20 


1 
1 








1 














90 


|_ 






1 


1 
1 














10 


1 
1 






1 


1 

1 












1 1 1 


100 




' ' ' ' II ' 
II 1 1 






1 






1 1 


1 


1 1 1 


1 1 1 1 




. 
I 


" - -d dP pggc 

Particle Size Diameter in Millimeters 




Coarse Aggregate 


Coarse Sand 


Fine Sand 


1 
Silt Clay 





FIGURE 15. - Grain size accumulation curves for samples 6 and 7. 



21 



c 

r 








MECHANICAL ANALYSIS GRAIN SIZE ACCUMULATION CURVE 






: - ^ - •»■ <N 5 ■* 


Sieve Sizes - U.S. Standard 

r CO? $eas§s 1 i§ 


100 




' 


1 








~^\ 




1 1 






T ' T 


'111 




10 














' 


^ 


k 1 1 




i 




II 1 1 




90 
















^ 


\ 




/ 




Mil 
1 1 1 1 




20 


















\ 


— 1 


/ 




Mil 




80 
















-\ 


\ 


/ 






1 1 II 




30 


















\ 


/ 






II II 




70 


















\ 


1 






ill! 




c 40 












1 






\ y 








II II 




60 1 












1 






1 \ / 








1 1 1 1 




0) 

0^ 50 

c 


















\ / 








1 1 1 1 
1 1 1 1 




50 t 

c 


















\ / 








MM 




e 60 


















¥ 








II II 




o 
40 5; 

Q. 


- 


SAMPLE 8 


1 












1 


n 






II 1 1 
1 II 1 




70 


1 












1 1 








MM 




30 


I 




















1 M 1 




80 


\ 












1 1 








MM 
Ml! 




20 


1 




















Mil 




90 


1 




















i M 1 

1 1 1 1 




10 


1 










■ 










MM 
1 1 II 




100 




1 II 'Ml 
II 1 1 1 1 






1 


1 




L _ 1 . 1 






i 1 1 


Mil 


1 1 1 




Particle Size Diameter in Millimeters 1 




Coarse Aggregate 


Coarse Sand 


Fine Sand 


Silt 


Clay 





c 







MECHANICAL ANALYSIS GRAIN SIZE ACCUMULATION CURVE 






2" 
1 1/2" 

1" 
3/4" 

1/2" 

3/8" 
1/4" 


Sieve Sizes - U.S. Standard 

_. (OOOOO o o^- 
r 00° ^<Mco¥<o T- cgcNj 


100 




1 ' I I 


I 


' 


^. 


1 
1 




I ' ' 


1 


' i 1 


1 1 1 1 


T 1 1 


10 










^ 










— 1 








90 












\ 






k 


1 / 








20 












\ 






^ 








80 












' \ 


I 

_1 J 




T 
1 




1 1 II 




30 














V 


/ 




1 








70 














> 


f 




1 

1 








S 




















1 








O) 

60 i 


c 40 




■ 1 — )■ — 1 f ■ 














1 
1 








« 


















1 








50 t 

c 


"■ 50 


















1 








0) 

y 60 

a. 
70 
















1 1 1 


1 








o 

40 a 

a. 


— 


SAMPLE 9 


1 
1 












1 
1 








1 












1 








30 


1 

1 












1 
1 










80 


1 












1 








90 


I- 
1 






















90 


1 












1 
1 








10 


1 — ' 
1 












1 








100 




' ' ' 1 1 1 

II 1 1 






1 




1 1 1 


1 
1 


1 1 1 






. 

5 


Particle Size Dianneter in Millimeters 




Coarse Aggregate 


Coarse Sand 


Fine Sand 


Silt 


Clay 





FIGURE 16. - Grain size accumulation curves for samples 8 and 9. 



22 



c 










MECHANICAL ANALYSIS GRAIN SIZE ACCUMULATION CURVE 






Sieve Sizes - U.S. Standard 


100 




T 






^ 


1 
1 


I 
1 




I 1 
1 1 


1 / 


1 i 1 


'111 


1 1 1 


10 










\, 


1 
1 


1 


-\ 


1 1 
1 1 


/ 








90 










S 


1 
1 


1 

1 


; 


^ 


/ 










20 












t^. 


1 


f\ 


S 


r 










80 












i ^. 


y 




|\ / 












30 












1 ^ 
1 


y 




1 ^^ 












70 












1 


T 




1 












T3 

a> 
c 40 












1 
1 


1 
1 




1 1 
1 1 












60 i 

(0 












1 


1 




1 1 












0) 












1 


1 




1 1 












to 

50 t 

c 


•^ 50 












1 
1 


1 

1 




1 1 












ii 60 












1 


1 




1 1 












o 
40 £ 

Q. 


^ 


SAMPLE 10 


1 






1 


1 




1 1 














1 






1 


1 




1 1 












30 


70 


1 






1 


1 




1 1 














1 

1 






1 
1 


1 




1 1 












20 


80 


1 — 
1 






1 


1 




1 1 












90 


1 






1 
1 


1 
1 




1 1 
1 1 












10 


1 
1 






1 


1 




1 1 
1 1 












100 




II 1 1 1 1 






1 


1 




1 1 






1 1 1 


1 1 1 1 






>" - -d dP pgog 

Particle Size Diameter in Millimeters i 




Coarse Aggregate 


Coarse Sand 


Fine Sand 


Silt 


Clay 





FIGURE 17.- Grain size accumulation curve for sample 10. 






FIGURE 18. - NX-size cores of four gunite specimens. 

The laminated zones are thought to have 
been caused by (1) poor hydration of the 
dry-mix gunite during recurrent spurting 
pulses of the nozzle, (2) flow pulsing of 
the dry-mix through the hose, (3) erratic 
loading of the rotating load chamber feed 
cells in the rotary dry-mix gun, (4) noz- 
zle operator water level control varia- 
tions , or perhaps a combination of all 
four factors. Sandy grains could easily 
be picked out of the laminae by finger- 
nail, even after 28 days of curing. The 
wet-mix samples did not contain the 
strength-reducing laminae. 



Cores cut for compressive strength 
testing were NX sized, 2.1 in in diameter 
and 4.2 in long. The strength of cored 
samples is greatly influenced by the 
maximum size of the contained aggregate. 
The rule of thumb for concrete-cored 
specimens is that the core diameter ratio 
should be at least three times the maxi- 
mum aggregate size, as was the case for 
all the fibered-gunite specimens. Addi- 
tional testing was performed using cubes. 

The flexure test specimens were made by 
gunning directly onto a wooden panel 
which contained 4- by 4- by 14-in molds. 
The molds were coated with form-release 
oil to prevent rapid water loss through 
absorption. The glass-f ibered products 
were uniform in cross section; however, 
the steel-f ibered products had a slight 
paucity of fibers at the bottom of the 
samples owing to rebounding and contained 
laminations. Additional flexure strength 
samples were acquired in 3- by 3- by 12- 
in sawn beam form. 

An initial effort was made to collect 
gunite samples for use in splitting 
tensile strength (Brazilian) testing. 



23 




FIGURE 19. - Wet-mix gunite sample acquisi- 
tion for splitting tensile analysis. 

Six-inch-diameter by 12-in-long plastic 
molds were utilized. Extreme difficulty 
was experienced in gunning the sample 
containers when dry-mix products were be- 
ing sampled. Samples of the wet-mix gun- 
ite could be slowly pumped into the cyl- 
inders, as shown in figure 19. Subse- 
quent sample testing of the dry-mix prod- 
ucts revealed multiple laminations , air 
pockets , bleed-out exterior scale (around 
the sides of the cylinder) , and other 
problems. Figure 20 shows typical cylin- 
ders of six different dry-mix products. 
Four of the six shown are defective. 



Splitting tensile strength was 
mined using the formula 



deter- 




1^ 



FIGURE 20. - Six-inch-diameter by 12-in-long 
cylinders of six different gunite products. 



2P 



a='rrLD 



where P is the maximum pressure applied 
and L and D are length and diameter re- 
spectively. The splitting tensile 28-day 
strengths observed ranged from 350 to 400 
psi for the fiberglass-fibered dry mixes, 
to 500 psi for the steel-f ibered dry 
mixes, to almost 800 psi for the high- 
strength silica fume wet-mix gunite. The 
data are not presented herein to prevent 
misleading correlations or comparisons. 
The splitting tensile strength testing of 
the gunite products was abandoned since 
collection methodology inconsistencies 
(cylinder rodding, tamping, tapping, and 
shooting or pouring) began to develop and 
comparative analysis would not have been 
meaningful. Sample acquisition problems 
render the engineering test misleading in 
comparing f ibered, pneumatic gunite prod- 
uct strengths. The test is not recom- 
mended for dry-mix gunites. 



REBOUND ANALYSIS 



The pneumatic application of f ibered, 
portland-cement-based gunite imparts ben- 
eficial compaction characteristics to the 
finished gunned product. The application 
technique, however, causes a relatively 
high percentage of the high-velocity ag- 
gregate and fibers (if metallic) to 
bounce or rebound off the fresh rock sur- 
face until a layer of cohesive material 
has accumulated there and can cushion the 
impact. ACI Standard 506-66 (Recommended 



Practice for Shotcreting) approximates 
shotcrete rebound generally as 15 to 30 
pet for sloping and vertical walls and 25 
to 50 pet for overhead work (l) . Gunite 
with fine-sized aggregates must be able 
to meet or hopefully exceed these percen- 
tages to be economical. 

When steel-fibered gunite is applied 
to a hard rock surface, such as massive 
limestone or silica-bearing strata (as at 



24 



the Lake Lynn Laboratory Mine) , sparks 
are commonly observed to occur at the 
fiber-rock contact. High-speed photogra- 
phy conducted in one experiment showed 
that many of the steel fibers were in the 
outer portion of the airstream and that 
many of them were blown away radially 
from near the point of intended impact 
shortly before or after they hit (19) . 
For high-velocity gunite work, the coarse 
aggregate particles (and fibers) con- 
tained in the pneumatic feed travel at 
such a high velocity (reportedly 300 to 
400 ft/s) (20) that they can inflict se- 
vere eye injury when they ricochet off 
the application surface. When suitable 
protective gear is used in conjunction 
with adequate precautionary measures, 
however, the safety aspects of the term 
"rebound" are upstaged by a more real- 
istic concern — that being the economic 
issues. 

Rebound is, in fact, waste. It cannot 
be reused or reprocessed. Except for 
that portion of rebound attributed to 
slough-off, the material is generally de- 
ficient in one or more of the necessary 
ingredients contained in the original 
composite mixture and must be discarded. 
In some applications , the gunning opera- 
tion must be halted to clean areas of the 
application surface that have been down- 
graded by the accumulation of aberrant 
rebound. If cleaning is not performed, 
loss of bond will occur in the final 
product. This problem is seldom cri- 
tical, however, in mining applications 
since the majority of the rib-roof appli- 
cations involve vertical or horizontal 
applications. 

The application of high-quality fibered 
gunite by an inexperienced crew using 
poorly maintained equipment and/or incor- 
rect pressure (air and water) settings 
can easily result in rebounds approaching 
50 pet. With a well-trained crew, the 
most effective means to reduce rebound 
include reduction of air pressure, use 
of more fines, use of shorter fibers 
(steel), predampening , and shooting at 



the wettest stable consistency ( 19 ) . Re- 
bound can also be reduced, according to 
the results of this investigation, by 
using more cement, finer aggregate top 
size, and silica fume, crushed slag, or 
fly ash. 

The term "rebound" draws at least two 
paradoxical thoughts to the minds of 
prospective gunite material users: 

1 . Although the term relates directly 
to the percentage of the purchased mate- 
rial that will result in useless waste, 
job specifications seldom address it 
specifically. 

2. Since rebound is an elusive prop- 
erty to quantify, the applications per- 
sonnel generally estimate about 15 pet, 
which, in this author's opinion, is very 
hard to achieve, particularly for the 
dry-mix gunite, unless an extremely pro- 
ficient gunning crew performs the work. 

Rebound calculations were performed on 
most of the products tested in the Lake 
Lynn Laboratory Experimental Mine. Sam- 
ples 11-17 were demonstrated at the manu- 
facturer's facilities and could not be 
tested for rebound percentage. Samples 
1-3 are wet-mix steel-f ibered silica fume 
gunite products containing a variety of 
ingredients that make the material more 
cohesive, resulting in significantly low 
rebound. The product manufacturer would 
not release accurate batch mix quanti- 
ties; therefore, a precise rebound per- 
centage could not be provided. Based on 
rebound cleanup comparisons, however, the 
rebound was estimated to be approximately 
10 pet. This is a significant improve- 
ment over conventional wet-mix shotcrete 
(without fiber, silica fume, or addi- 
tives) used in the past. An average re- 
bound of 47 pet was reported for a 6,618- 
psi-compressive-strength (28-day) wet-mix 
shotcrete used in an Arizona deep mine 
(21). Wet mining conditions were experi- 
enced during that particular application, 
however, and shotcrete accelerators were 
even found to be ineffective. 



25 



For the 
formulas : 



dry-mix prebagged products, rebound was calculated using two different 



A. Rebound (pet) = 



gunite rebound collected (wet, lb) 



Dry gunite shot (lb) + )-^ — ags gum e s o ^(cgjae^t ^i^/yd3)(^ater-cement ratio) 

(No. bags/yd-' ) 



X 100. 



B. Rebound (pet) = 



gunite rebound collected (wet, lb) 



dry gunite shot (lb) + [(yd^ of gunite shot) (300 lb water/yd^)] 



X 100. 



Formula A assumes the specified water- 
cement ratio was achieved in the gunning 
operation. 

Formula B assumes that 1 yd^ of gun- 
ite weighs 4,000 lb and contains 3,700 lb 
of solids and 300 lb of water. Normal- 
ly, gunite products weigh from 143 to 
154 Ib/ft^, resulting in a range from 



3,861 to 4,158 lb/yd3; 4,000 Ib/yd^ is 
frequently used in gunite quantity 
calculations. The development and use of 
these formulae for this investigation 
were required owing to unavailability of 
direct measurement of the water factor. 
Although the rebound percentages calcu- 
lated and presented in table 5 are based 



TABLE 5. - Gunite rebound percentages 



Sample 



Gunite shot (wet) , 
lb 



Rebound (wet) , 
lb 



Rebound , pet 



Formula A Formula B 



1-3. 
4.. 
5., 
6., 
7., 
8., 

9., 

10., 



0) 

8,850 
1,350 
6,960 
3,540 
2,050 
7,500 
11,040 
5,760 



NA 

(2) 

NA 

1,050 

850 

1,090 

1,500 

1,900 

1,020 



®10 


NA 


32 


33 


NA 


NA 


13-14 


3i4 


21 


22 


H3 


449 


18 


18 


15 


16 


16 


16 



^Estimated. NA Not available. 

^Samples 1-3 are wet-mix gunites. With the number of additives included, the mate- 
rial is extremely cohesive. Precise "shot" material weights were not provided by the 
manufacturer; rebound calculations are, therefore, not available. Comparatively 
(based on empirical observation) , the rebound mainly consisted of steel fiber and a 
small amount of coarse aggregate and was significantly lower in quantity than for any 
of the dry-mix types. An estimate of 10 pet is conservative. 

^3,550-350=3,200. Included in the rebound calculation is a 20-in by 5-ft by 3-in- 
thick roof spall-off zone. At a density of approximately 2.1 g/cm^, the mass weighed 
approximately 274 lb. Two other spall zones contributed to a total of approximately 
350 lb of spall in the rebound calculation. 

^Extreme dust occurred at the gun. The calculated rebound is estimated to be low 
by 3 to 5 pet. True rebound percent, therefore, may approach 20 pet. 

^Very high dust occurred at the gun; also, the material exhibited very high slump. 
The manufacturer does not recommend pneumatic application, but rather, trowel appli- 
cation. The pneumatic application technique for this product was conducted for test- 
ing purposes only. 

^Product 9 was shot in 2 separate applications, each having rebound collection 
performed. 



26 



on actual rebound collected and weighed 
(fig, 21), they may be slightly higher or 
lower than actual owing to one or more of 
the following: 

1. Errors included in physically shov- 
elling up the rebound from the flat con- 
crete mine floor. 

2. Errors due to weighing the rebound 
on a truck scale (reported to be accurate 
to 10 to 15 lb). 

3. Use of an assumed water-cement ra- 
tio of 0.4 in the water weight calcula- 
tion, when more or less water may have 
been used during application. It is im- 
portant to note, however, that a water- 
cement ratio change from 0.4 to 0.5 in 
the calculation changed the rebound per- 
centage factor only 1 or 2 pet. 

4. The specific gravity of the rebound 
differing considerably from that of the 
in-place product. 

5. Dewatering, bleeding, or dessica- 
tion of the collected rebound mass before 
physical weighing. 

6. The ventilation-borne gunite dust 
not being "estimated" and removed from 
the "dry gunite shot (lb)" factor in the 
divisor segment of the rebound equations. 




The factor used, therefore, results in 
slightly lower than actual rebound per- 
centages for those products with very 
little dust loss and in significantly 
lower than actual rebound readings for 
those products with extreme dust. 

The complete listing of rebound data 
used in the calculations is shown in ap- 
pendix A. The mean dry-mix rebound per- 
centage for all products tested, exclud- 
ing the lowest and highest values, was 
20.4 pet (std dev=±6.8) using values from 
formila A and 21 pet (std dev=±7.1) using 
formula B values. 

One additional comparative test was 
performed to determine the ratio of roof 
rebound to rib rebound. Based on the 
findings of the comparison analyses (of 
one company's application), the roof -rib 
rebound ratio was determined to be ap- 
proximately 2:1 for one product. Angled 
roof gunning such as is shown in figure 

22 results in very high rebound. Figures 

23 and 24 show more efficient roof gun- 
ning positions. 




FIGURE 21. - Gunite rebound collected and 
ready for weighing. 



FIGURE 22. = Angled roof gunning produces 
very high rebound. 



27 





FIGURE 23. = Near=vertical wet-mix roof gun- 
ning gives low rebouncl = 



FIGURE 24o = Near=vertical dry=mix roof gun= 
ning with reduced pressure gives low rebound. 



GUNITE DUST 



The Federal Coal Mine Health and Safety 
Act of 1969 required that deep coal mines 
maintain their airborne respirable dust 
(nominally less than 5 to 10 ym in size) 
concentration at or below 2.0 mg/m^ over 
an 8-h average time period after December 
30, 1972 (22). When the respirable dust 
in the mine atmosphere of active workings 
contains more than 5 pet quartz , the res- 
pirable concentration allowable is re- 
duced significantly. The concentration 
in milligrams per cubic meter is computed 
by dividing the percent of quartz pres- 
ent into the number 10 (23^) . Total dust 
loading is required to be less than 10 
mg/m^ in metal and nonmetal mines {2A) . 
Consequently, all deep mining activities, 
including gunite application, must be 
performed in consideration of the total 
respirable dust generated. Coal workers' 
pneumoconiosis ("black lung"), asbesto- 
sis, and silicosis are of primary con- 
cern, therefore total dust exposure, re- 
gardless of its composition, is monitored 
by mine regulatory agencies. 



Dust sample collection and analysis 
were performed during gunite emplacement 
for all four companies participating in 
the comparative research. The dust moni- 
toring was performed in the following 
manner and with the equipment shown in 
figure 25. 

1. Dust sampler — filter assemblies 
used were Dupont model P-2500 low-volume 
gravimetric air samplers fitted with cy- 
clones (for respirable dust measuring) 
and 1-1/2-in diam MSA gravimetric cas- 
sette membrane filters. The sampler is a 
constant-flow model with an automatic 
flow control system that maintains con- 
stant airflow rate within ±5 pet over 
pressure drop changes up to 15 in. The 
samplers have a range of 1,000 to 2,500 
cm^/min. A pump flow rate of 2,000 cm^/ 
min (2 L/min) was used in this investiga- 
tion. The cyclone-filter holder assembly 
is designed to simulate the human respi- 
ratory tract in its selectivity for the 
respirable fraction of dust particles. 



28 




FIGURE 25. - Gunite dust monitoring equipment. 



The lO-tnm cyclone assembly separates out 

the dust particles larger than 10 ym. 

The membrane filter traps the particles 
smaller than 10 ym. For the "total dust" 

sample collection, the cyclone was 

omitted from the assembly and only the 

air sampler pump and filter assembly were 
used. 

2. Six filter assemblies were sus- 
pended from the mine roof a nominal dis- 
tance of 60 in above the mine floor and 
85 to 90 ft downdrift of the gunite ap- 
plication zone. The gun loading area 
(the major dust loading area) was 15 to 
25 ft updrift from the nozzle-application 
zone; i.e., a minimum of 100 to 110 ft 
updrift of the samplers. 

3. Cyclones were used on two of the 
six downdrift samplers. 

4. Three filter assemblies (without 
cyclones) were suspended 60 in above the 
mine floor 135 ft updrift of the gunite 
application zone in clean mine air to es- 
tablish ambient total dust levels. A 
control filter was provided at the up- 
drift location during the application of 



some gunite products. The filter ori- 
fices were opened and exposed to the mine 
air to evaluate the amount of moisture 
absorption and other prospective filter 
weight increases not related to the dust 
sampling, 

5. The mine temperature, relative hu- 
midity, and ventilation conditions were 
monitored to provide comparison charac- 
teristics of the collected data. The 
100-hp axivane ventilation fan was main- 
tained on fourth speed forward during all 
gunite applications. Bulkhead doors were 
maintained in the full-open position. 
The mine drift containing the gunite 
equipment received 50 pet of the avail- 
able 60,000 ft3/min of air (30,000 ftV 
min) . 

6. Air sampling periods were carefully 
timed. 

7. Gunite specimens 11 through 17 were 
gunned during a demonstration at the man- 
ufacturer's facilities and, therefore, 
were not monitored for dust data. 

Gunite application equipment , particu- 
larly the dry-mix type, is notoriously 
dusty. Although a concerted effort has 
been made by the gunite equipment manu- 
facturers to reduce gun dust, the problem 
has been only marginally reduced for most 
dry-mix gun types. Ventilation air dust 
loadings result from three separate seg- 
ments of the underground gunite appli- 
cation operation. The major dust con- 
butor was found to be the gun hopper 
loading operation, in which 50- to 80-lb 
paper bags of premixed gunite are opened 
either manually or by the use of a gun 
hopper knife, and dumped into the hop- 
per — sometimes through a screen or griz- 
zly to prevent clogging by lumps , fiber 
balls, or other foreign materials. The 
bag ripping, emptying, and shaking opera- 
tion is a serious dust generator, 

A second serious dust generator, par- 
ticularly in the rotary, continuously 
loaded dry-mix gunite gun, is the rotat- 
ing airlock (rotor). The rotor takes 
the dry gunite material from atmospheric 



29 



pressure in the feed hopper, measures out 
a slug of the product, and injects it 
into the gunite placement hose under 
pressure where a moving high-pressure 
airstream (40 to 90 psi) carries it to- 
ward the nozzle. In poorly maintained 
guns in which either the rubber wear 
plates, steel friction plates, or both 
are worn or misaligned , a cyclic pulse of 
gunite is puffed out of the rotor area 
(and sometimes even the hopper area) each 
time a chamber slug is emptied into the 
hose. 

Three of the companies involved in the 
gunite comparative research used dry-mix 
rotary guns. One company experienced se- 
vere dust generation problems due to worn 
wear and/or friction plates. Figure 26 
shows gunite dust caused by bag unloading 
and hopper puffing. Figure 27 shows the 
same gun after the gunning operation was 
completed. When gunning was completed, 
dust thicknesses (from the malfunctioning 
gun) of approximately 1/16 in were found 
on the upper surface of air samplers sus- 
pended from the mine roof 100 ft down- 
drift. Not only was dust pulsing from 
the rotor section of the gun, the loading 
hopper was casting loaded gunite back 
out of the hopper in large puffs, allow- 
ing the moving mine ventilation air to 



separate and carry the fines (e.g., ce- 
ment fraction) downdrift, much like the 
process used in nonautomated farming 
areas to separate chaff from wheat on a 
windy day. Some gunite samples collected 
during the gun malfunction period were so 
lean (cement-poor) they could be crumbled 
by hand. 

A third dust source characteristic of 
dry-mix gunite application is pneumati- 
cally ejected dust from the nozzle due to 
incomplete hydration at the nozzle water 
ring section. The internal mix water 
spray through the nozzle water ring is 
controlled manually by the nozzle opera- 
tor, who must gauge water addition empir- 
ically, based on the glisten of the ap- 
plied product as observed in the poorly 
lighted conditions of the mine. The noz- 
zle operator is under constant pressure 
to maintain a low water-cement ratio to 
achieve optimum strength characteristics 
of the product , while at the same time 
making sure the water added sufficiently 
hydrates the port land cement fraction. 
Since most of the rotary guns tested 
characteristically cough, speed up, slow 
down, sputter, and pulse, the nozzle 
operator must make continuous water ad- 
justments to prevent dusty (too dry) or 
slough-off (too wet) gun operation. 




FIGURE 26. - Gunite dust from the gun-loading 
operation. Gun malfunction was partially the 
cause of the excessive dust. 




FIGURE 27. - Gunite gun dust (fines) on mine 
floor caused by worn friction plate or wear pad 
(or both). 



30 



Double-chamber guns (in which an upper 
chamber is intermittently loaded while a 
lower chamber is continuously flowing) , 
single-batch guns , and gunite predampener 
feeders are known to reduce dust loading 
of mine air if space conditions and bud- 
get permit their use. However, none were 
demonstrated in this effort. 

Table 6 summarizes the dust data; full 
data are presented in appendix B. For 
the "total" dust collected, the table 

"Total" dust in air = 



(0 



provides an analysis of dust collected 
per unit time (mg/min) , dust collected 
per unit weight of dry gunite fed through 
the gun (mg/ lb shot) , and dust collected 
per unit volume of air moved through the 
sampler (mg/m^ in air). The latter fig- 
ure may be the most meaningful and was 
calculated by dividing the weight of dust 
collected by the volume of dust-laden air 
moved through the sampler pump for the 
duration of the sampling period : 

1.57 mg 

.002 m^/min) x 167 min 



4.70 mg/m^. 



Some of the dust loadings are extremely 
high. Though they appear to violate the 
permissible standards (2 mg/m^), they 
must be taken in context of the fact that 
the standards are given for an 8-h shift. 
If the gunite equipment was the only sig- 
nificant dust generator, the worst case 
(sample 6) for the time period operated 
(70 min) generated 99.2 pet of the allow- 
able 8-h loading. 

In comparing the gunite product dust 
data, the following should be considered: 



function of crew operation (hopper load- 
ing and nozzle operation) and the mechan- 
ical condition of the gun. The products 
were quite similar in dust constituent 
content. 

2. The wet-mix products were dumped 
into a mixer from bags, generating a ma- 
jority of the products' dust. Very lit- 
tle of the wet-mix product dust was from 
the nozzle. The mixing operation turned 
out to be quite dusty compared to some 
dry-mix operations. 



1. Dry-mix gunite product dust load- 
ing differences were found to be a 



3. Neither the respirable nor the to- 
tal (nuisance) dust loadings exceeded the 



TABLE 6. - Gunite dust data 



Sample 


Gunite 
shot, 
lb 


Time, 
min 


Respirable 

dust (av) , 

mg 


Total 
dust (av) , 
mg 


Total dust, 
mg/min 


Total dust 
per pound 
shot, mg 


Total dust 
in air, 
mg/m^ 


3I 

42 

4 

5 

6 

7 

8 

9 

10 


4,200 
9,000 
8,500 
1,350 
7,680 
3,840 
2,400 
8,700 
11,360 


167 

180 

125 

60 

70 

38 

55 

55 

102 


0.87 
.37 

4.81 
.03 

1.71 
NA 

1.60 
.04 
.06 


1.57 
8.03 
7.97 

.37 
9.53 

.59 
3.45 

.34 
1.10 


0.9 X 10-2 

4.4 X 10-2 
6.3 X 10-2 

.6 X 10-2 
13.6 X 10-2 

1.5 X 10-2 
6.2 X 10-2 

.6 X 10-2 
1.0 X 10-2 


3.7 X 10-*^ 
8.9 X lO-'* 

9.4 X 10-*+ 
2.7 X 10-^+ 

12.4 X 10-*+ 

1.5 X lO-'* 
14.4 X lO-'^ 

.4 X lO-^t 
1.0 X lO-'^ 


4.70 
22.30 
31.16 

3.08 
68.07 

7.76 
31.36 

3.09 

5.39 



NA Not available. 

^Volume of wet-mix type 3 estimated at 1.05 yd^. At an estimated 4,000 lb/yd ^, the 
total shot is 4,200 lb. 

2two separate applications of product 4 were monitored for dust loading. 



31 



standards for dust when taken in context 
of an 8-h shift (480 min) . However, at 
least four of the eight dry-mix samplings 
produced loadings that would exceed the 



standards if the crew were to gun at that 
loading rate for a full shift or if they 
were gunning near a working section. 



SCANNING ELECTRON MICROPROBE ANALYSIS OF SILICA FUME 



An electron probe microanalysis was 
performed on the silica fume and cement 
fractions of sample 3, to investigate the 
particle size relationship (with cement) 
and angularity of the silica fume as it 
relates to respirable dust loading, A 
qualitative elemental chemical analysis 
was also performed both on the silica 
fume and on portland cement because of a 
concern that some ferroalloy fume byprod- 
ucts, from which silica fume particles 
are concentrated, contain relatively high 
concentrations of toxic chromium and/or 
cadmium when condensed from a furnace 
burden melt containing those metals. 

Figure 28 reveals the size relationship 
between cement (large particles) and sil- 
ica fume (small particles). Although 
some of the silica fume particles appear 
to be somewhat angular, they are, in 



fact, agglomerations of smaller, amor- 
phous particles, as shown in figure 29, 
Silica fume size (diameter) ranged from 
0,1 to 1 ym. The silica fume was also 
analyzed in an XRD-5 X-ray dif f ractometer 
and found to exhibit no characteristic 
quartz (Si02) peak when bombarded with 
copper K°^ radiation. Absence of the peak 
confirms the amorphous nature of the 
material. 

The silica fume partice size is in 
the range of respirable dust. Its amor- 
phous surface characteristics and wet- 
mix incorporation method into the gun- 
ite, however, reduce the major potential 
silicosis concerns. The bag opening 
function for bulk mixing of the silica 
fume or prebag mix, however, should al- 
ways be performed using dust protection 
equipment , 





FIGURE 28. = Scanning electron microscope mi» 
crophotograph of portlond cement and silica fume. 



FIGURE 29. - Scanning electron microscope mi- 
crophotograph of silica fume. 



32 



An elemental qualitative chemical anal- 
ysis was performed on the silica fume and 
Portland cement using a scanning electron 
microscope (SEM) and an energy-dispersive 
X-ray (EDX) analyser. A small amount of 
the sample was supported on a metallic 
substrate, which was then inserted into 
the SEM's sample chamber. The X-ray pho- 
tons produced by the bombardment of the 
sample by electrons are detected by a 
solid state detector. The output signal 
of the detector is fed into a multichan- 
nel analyzer where the signals are sorted 



according to energy to produce an X-ray 
spectrum. The energy of the X-ray is 
related to the atomic number of the atoms 
present in the sample. The elemental 
species present are, therefore, identi- 
fied by the X-ray signals' different 
energies. 

Tables 7 and 8 present the count data, 
energy readings , and the representative 
elements associated with the various en- 
ergy spectra peaks shown in figures 30 
and 31 respectively. 



TABLE 7. - Element X-ray spectrum data for silica fume 



Energy , keV 


Element 


Count rate 


Energy , keV 


Element 


Count rate 


1.5 
1.74 


Aluminum 

Silicon. ........ 


NA 

3,491 

47 

67 


3.7 
4.5 
5.4 
6.4 


Calcium (K°:) .... 

Titanium 

Chromium 

Iron 


57 
45 


2.3 


Sulfur 


45 


3.3 


Potassium 


38 



NA Not available (unmeasurable) . 



TABLE 8. - Element X-ray spectrum data for cement 



Energy , keV 


Element 


Count rate 


Energy, keV 


Element 


Count rate 


1.5 
1.74 


Aluminum 

Silicon. ........ 


172 
816 
289 
219 


3.7 
4.0 
4.5 
6.4 


Calcium (K«) .... 
Calcium (Kg) .... 

Titanium 

Iron 


4,971 
775 


2.3 


Sulfur 


73 


3.3 


Potassium 


146 



NOTE: Calcium exhibits 2 detectable peaks (K°: and Kg) when it occurs in high 
concentrations . 



1,0 



800 



CO 

h- 

§ 600 

o 
o 

UJ 

^ 400 

Q- 



200 








"T r 



Off scale, 
total count 4,971 



Total count time 
175s 



Note^ 
graphically reproduced 
from microphotograph. 




500 



4 6 

ENERGY, keV 

FIGURE 30. - Electron probe microanalysis of 
Portland cement. 



400 - 



CO 

I- 

i 300 

o 

o 



UJ 
CO 



200 



00 







Off scale, total count 3,491 



Total count tinne, 200 s 



Note= graphically reproduced 
from microphotograph 




4 6 

ENERGY, keV 

FIGURE 31. - Electron probe microanalysis of 
silica fume. 



33 



Elements of low atomic number such as 
are found in both the cement and silica 
fume are difficult, at best, to identify 
in a quantitative manner using conven- 
tional X-ray emission spectrographic 
equipment where the sample is bombarded 
directly by X-rays. This is due to the 
high background, absorption (X-ray), and 
enhancement effects. In the silica- 
alumina system, for example, silicon K"^ 
is strongly absorbed by aluminum to ex- 
cite aluminum K<^; the mass absorption co- 
efficient in this case exceeds 3,000. 
With an increasing content of alumina, 
the intensity of silicon K°^ decreases 
progressively. The intensity of alumi- 
num K°^ behaves quite differently as the 
silica content decreases (25) . Addi- 
tionally, the relatively high background 



tends to hide 
chromium . 



some elements , such as 



By using a focused electron beam from 
the SEM rather than X-rays to exite atoms 
in the sample into producing essentially 
a point source of strongly divergent 
X-rays, as was used here, absorption and 
enhancement effects are minimized. The 
analyses produced by the technique, how- 
ever, are purely qualitative and should, 
in this case, be used only to indicate 
the presence or absence of an element and 
its relative composition. The analysis 
presented indicates that some chromium 
occurs in the silica fume but in very low 
concentration. Cadmium was not detected 
in the sample. 



COMPRESSIVE STRENGTH ANALYSIS 



The fibered-gunite products were ana- 
lysed for unconfined uniaxial compressive 
strength using conventional testing pro- 
cedures. Samples 1-10 were tested by the 
Bureau with additional analyses provided 
by Pittsburgh Testing Laboratories. Sam- 
ples 11-17 were tested by the Froehling 
and Robertson, Inc. , Engineering Labora- 
tory. For samples 1-10, full-length NX- 
sized cores up to 8 in long were drilled 
out of 24-in by 24-in by 8-in-thick sam- 
ple blocks, and the best 4.2-in specimens 
were selected and trimmed out. The near- 
bottom and near-side areas of the sample 
blocks were avoided in specimen selection 
since they have high rebound (low fiber 
and smaller aggregate characteristics). 
Additionally, laminated sections were 
avoided. Although an average of 15 cores 
were taken from each product sample 
block, some were so laced with lamina- 
tions that specimens had to be tested 
that contained minor laminations. Al- 
though this procedure may not be con- 
doned by the industry, which strives to 
obtain perfect samples to provide optimum 
strength characteristics, the use of lam- 
inated samples may provide a more realis- 
tic analysis of the product that was ap- 
plied underground. 

Core length was maintained at twice 
the diameter. Correction factors for 



long or short cores were, therefore, 
unneeded. The length cuts were made with 
a precision-self-feeding diamond saw 
blade in order to obtain compression 
bearing surfaces perpendicular to the 
long axis of the cores. Compressive 
strengths were analyzed by using a 
120,000-lb pressure Tinius Olsen machine 
(fig. 32). A 2.13-in-diameter stainless 
steel, two-piece, universal rotating 
bearing block was used to overcome minor 
offset loading (fig. 33). 




FIGURE 32. . Tinius Olsen 120,000.Ib test- 
ing machine used in gunite analysis. 



34 



Compressive strength tests were also 
performed on sawn cubes of some samples. 
The analyses were performed by testing 
laboratories and funded by gunite prod- 
uct manufacturers. It is important to 
note that ACI Standard 506-66 indicates 
that "cube strengths may be reported as 
length/diameter or (L/D) determined or 
converted to cylinder (L/D=2) strengths 
by multiplying by the factor 0.85" 
(_1_) . As contained in this report , the 
strengths have not been converted. Addi- 
tionally, it has been reported (26) that 
the percentage reduction in strength of 
drilled cores from concrete increases 
with the increase in strength level of 
the concrete. The reason given is that 
stronger concrete offers more resist- 
ance to drilling, whereby microcracks or 
other damages are introduced into the 
core. If this is true, then the drilled 
cores used by the Bureau in this inves- 
tigation would produce lower ultimate 
compressive strengths for the higher 
strength products than are produced from 
the larger cubes normally used at testing 
laboratories. A Bureau-performed com- 
pressive strength analysis, therefore, 
may be more than 15 pet lower than an 
analysis received from a licensed testing 
laboratory for an identical specimen. 




FIGURE 33. = Stainless steel rotating bearing 
block used in gunite core compressive strength 
analysis. 

Compressive strengths of the specimens 
were derived by the standard formula 

compressive strength = — '" —^ -> 

where P{max) = maximum applied load, 

lb. 



and 



r = radius of core, in. 



The compressive strength of the samples 
tested as cubes was derived using the 
formula 



compressive strength = 



P( ma x) 



area (cross section) 



The applied compressive stress was con- 
tinued until observable fracture was 
noted and the stress-strain curve had 
peaked and established a definitive irre- 
versible negative trend after failure had 
occurred. Stress in this paper relates 
to the intensity of the internal compo- 
nents of the forces in the gunite that 
resist change in the form of the core. 
Strain refers to axial strain only in the 
direction of applied loading, since lat- 
eral strain or deformation was not mea- 
sured. Figures 34 and 35 are compressive 
strength diagrams of two gunite samples 
plotted with the applied load on the 



ordinates and compressive deflection on 
the abscissas, showing rapid and gradual 
failure, respectively. 

Although true hourglass or shear cone 
rupture was observed in some specimens at 
failure, this was a rarity. The random 
failure patterns observed were due to 
(1) the nonhomogeneous composition of the 
gunite, (2) the isotropic distribution of 
the fibers, and (3) the end section re- 
straint to lateral expansion caused by 
friction and/or loading of the platen and 
bearing block. 



35 




50,000 



£ 40,000 



2 3 4 5 6 7 

DEFLECTION (COMPRESSIVE), 0.01 in/in 

FIGURE 34. - Gunite compressive strength plot 
showing rapid failure. 

ASTM 39-66 recommends end capping for 
concrete cylinders that are not within 
0.002 in from plane (27) . For sample 
convexity of only 0.01 in in a cylin- 
der of 6-in diameter, tests have shown 
reduction in strength of up to 20 pet 
(28) . Accordingly, great effort was 
made. to obtain planar ends on the sam- 
ples by precision sawing. Slightly lower 
compressive strength ratings may have 
been obtained, however, since end cap- 
ping was not performed on the Bureau 
specimens. 

Compression samples 11-17 were sawn 
by the referenced testing laboratory 
from the test panels in 3-in cubes. 
According to the manager of the labo- 
ratory, the test panels were trimmed 
1-1/2 to 2 in to discard the high re- 
bound zone. The ultimate load was re- 
corded for compressive strength. Lami- 
nations were somewhat problematical, 
especially for sample 17. The labora- 
tory reported that the cubes tended to 
fail along dry lamination planes where 
present. 




2 5 4 5 6 7 

DEFLECTION (COMPRESSIVE ), 0.01 in/in 

FIGURE 35. - Gunite compressive strength plot 
showing gradual failure. 

Table 9 presents the compressive 
strength analyses of all specimens 
tested. It should be noted that three 
product manufacturers involved in the 
gunite demonstrations elected to have 
samples of their products (collected 
during the demonstration) tested at pri- 
vate testing laboratories. The validated 
analyses are included in this paper to 
provide comparative references . The 
higher strength readings recorded by the 
private laboratories are due to the fact 
the samples were cured in meticulously 
controlled (temperature and humidity) fog 
rooms, end capped, and tested in cube 
rather than cylinder form. The Bureau's 
testing results, though perhaps lower in 
overall value, were obtained from test- 
ing procedures that were carefully dupli- 
cated for all specimens . Owing to the 
presence of laminations in most of the 
gunite products tested by the Bureau, 
considerable latitude occurred in the 
test results. To offset this, the lowest 
compressive strength values were elimi- 
nated and the highest values were aver- 
aged and recorded. 



FLEXURAL STRENGTH ANALYSIS 



The fibrous gunite products were 
tested for flexural strength using the 
simple beam-third point loading methods. 
Bearing blocks were used to insure that 
the forces applied to the beams were ver- 
tical and without eccentricity. As near- 
ly as practicable, the test specimens had 
a span three times their depth plus a 



minimum of 1 in on each end. The Bureau- 
tested specimens measured 4 by 4 by 14 
in. Samples 11-17 were tested by a pri- 
vate testing laboratory and measured 3 by 
3 by 12 in. Samples 1-3, 6, and 7 were 
also tested at another private testing 
laboratory using a specimen size of 3 by 
3 by 12 in. 



36 







t^ vO 


CM 


H 


H 


H 


»* CO 


cy> 


E-i 


f-< i-i i-i 


H 


>. JJ 


4J 


4-1 


4J 


1 c (u 


1 t 




p-« 


CM ro 


CO 


Z 


Z 


z 


-3- CO 


00 


^ 


z z z 


Z 


C O 


O 


u 


o 


CO -H ^ 


a c 




,-H 


O CM 


^H 








-* CO 


00 








CO 3 


3 


3 


3 


4-1 1 4J 


O CO 




r-t 


#« «> 


#K 








^ tfK 


•. 








a-TS 


•O 


TJ 


T3 


4-1 CM 


tJ w 






ro fO 


CO 








<)■ CO 


CO 








e o 
o u 


O 

u 


O 
U 


o 
l-l 


PL( ^ O 


Crt 


























l-l 






CM r- 


in 


H 


H 


Ch 


so O 


00 


H 


H H H 


H 


o a 


a. 


a 


a 


1 


cu M 




^^ 


fO in 


<r 


Z 


Z 


fe 


vO -H 


CO 


2: 


Z Z Z 


Z 










<u f^ CO 


T) CJ 




f— 4 


-* <!■ 


<r 








\D »a- 


m 








M 








X Q) 


c <: 




^ 


#« #1 


#> 








#t fs 


•■ 








(U (U 


<u 


(1) 


0) 


4-1 a a 


•i-t 






<r -^r 


•<j- 








vO vO 


so 








fl5 

1-1 


4-1 


42 


4J 


O -H 
4-1 M 4-1 
CO IM 


rH C 
>^•H 
CJ 






•<r o 


CM 


H 


H 


H 


vo in 


-H 


^ 


H H H 


H 




LTl 


p~. in 


\o 


Z 


Z 


Z 


r-- vD 


r^ 


53 


z z z 


Z 


o >, 








4J 


-o 




^^ 


vO C30 


r«. 








in r-» 


i-H 








CuXi 


>^ 


s>% 


>% 


•o c 


M (U 




^ 


9. *. 


CO 








vo in 


SO 








0) T3 


^ 


^ 


X 


4-1 4-1 l-l 

CO bo a) 


O CO 
i»-4 CO 

3 




































CO ^ 


CM 


H 


H 


H 


O o 


o 


9—1 


H H H 


H 


W <U 


T3 


-C3 


T3 


(1) C UH 


•O O 




<!' 


vO -* 


in 


Z 


Z 


Z 


o\ in 


CM 


2 


z z z 


Z 


<0 -O 


0) 


(U 


0) 


4-1 0) M-l 


Q) CD 


x 


i-H 


rH -1 


^H 








in o 


CO 








iH C 


T3 


•a 


t3 


M -H 


4-1 -H 


o 


(— t 


#t ^ 


«> 








#^ •\ 


^ 








3 


C 


c 


C 


T3 4J -O 


l-l -o 






vO ^D 


vO 








so 00 


r~~. 








CO y-i 


3 

14-1 


3 
i*-i 


3 
iw 


C CO 

CO CM 


O 

Ou CO 
























^^^ 






O r~ 


^ 


H 


H 


H 


-H CM 


r«. 


H 


H H H 


H 


•o 








(U 


0) CO 


OJ 


CO 


CM vD 


CJN 


Z 


Z 


Z 


CO <r 


CO 


Z 


^: iz: z 


Z 


c 








> 4-1 


l-l 


M 


<— 1 


r~~ vO 


^ 








00 «3- 


so 








CO >» 


bO 


bO 


bO 


- iH CO 


0) 


to 


i-H 


^ #» 


- 








•t *> 


^ 








U 


C 


C 


C 


M CO 


CO iH 


3 




in vD 


^ 








so 00 


r~~ 








O 


1-1 

4-) 


•H 
4J 


•r-l 
4J 


O CO 4J 
X 0) O 


4-1 & 

CO a 
























CO 




vD —1 


ON 


H 


H 


H 


—1 sD 


(Js 


H 


H H H 


H 


O CO 


CO 


CO 


CO 


4J (J X 


O CO 




CvJ 


in o 


CM 


Z 


Z 


Z 


so CO 


a\ 


Z 


z z z 


Z 


X M 


0) 


cu 


0) 


3 a. CO 


CO 


u 


^-1 


—1 in 


00 








o in 


CM 








4J O 


4-1 


4J 


u 


CO e 




1) 


^H 


^ #^ 










•t as 


•t 








3 ^ 


^^ 


v-' 


■^x 


o 


• (U 


a, 




vo in 


in 








00 so 


p~. 








CO CO 








(1) u a> 


^ X 
C 3 



































CO 




00 ro 


v£> 


P— 1 


H 


H 


CM <• 


00 


H 


H H H 


H 


(U 


CO 


>> 


>^ 


4J 0) 


•H O 


T3 


^^ 


r^ r^ 


CM 


^ 


Z 


Z 


CO o 


so 


Z 


z z z 


Z 


X bO 


(U 


M 


M 


>^ S 




c 


•-H 


CM r^ 


o 








in 00 


so 








■u C 


•H 


o 


o 


t^ CO 


-H fH 


3 


.— t 


•> f^ 










•• 0s 










1-1 


h 


4J 


4-1 


/5 t3 4J 


• CO 


O 




\D in 


vO 








0\ <T< 


0^ 




. 




.Q CO 


o 

4J 


CO 


CO 
u 


1 CO 
TS 00 X 


CM O 




























o o 


in 


in 


O 


00 


-* O 


CM 


H 


H H H 


H 


(1) 


CO 


o 


o 


0) CM W 


4J 


* 




-H ^ 


r-^ 


CM 


CO 


CM 


-^ 00 


so 


Z 


Z Z Z 


Z 


•O H 


u 


XI 


^ 


4J 


Q) C 


CO 


o 


a> CM 


in 


m 


CO 


>a- 


C^ CO 


I-H 








<u 


o 


CO 


CO 


CO U 4J 


l-l CU 


C 


—1 


•K f« 


•K 


f. 


«t 




^ ^ 


•K 








JJ 


^ 


hJ 


hJ 


•H O O 


O T5 


a 




fO CO 


CO 


-* 


<■ 


<j- 


<f CO 


<1- 








CO C 

•--1 o 


CO 






CO U-l 3 
CO T) 


O -H 






























•H 




vO sD 


^H 


CO 


o 


r-~ 


-;j- 00 


SO 


H 


H H H 


H 


CO CO 




bO 


bO 


CO O 


CU 


U 




CM in 


ON 


00 




-* 


S3- sD 


O 


Z 


z z z 


Z 


CO *J 




c 


c 


(U U 


N C 


(U 


CT^ 


r~. O 


CO 


o 


00 


<r 


00 -H 


O 








CO M 


bO 


•H 


•H 


U Q. 


•H CO 


a 




^ m. 


#» 


^ 


» 


•\ 


» rt 


*• 








0) 


c 


4-> 


U 


- CO 


CO 


CO 




in in 


in 


in 


in 


in 


SO in 


sO 




.^_-___-_^^_,^^^_ 






•H 
4J 


CO 

(3) 


CO 
(U 


CO (U 

(u CO a 


1 U 

>< o 


























0) 




H H 


H 


H 


H 


H 


r-. i-~. 


1 — 


H 


H H H 


9—1 


CO Ki 


CO 


H 


H 


•H 4-1 CO 


Z >4-l 


4J 




2 Z 


z 


Z 


Z 


Z 


r^ o^ 


00 


Z 


z z z 


S3 


a) 


dJ 






4-1 CO CO 




•H 




Cvl CM 


CM 


Cvl 


CM 


Csl 


r-~ CO 


in 








•H <^ 


H 






•H Q 


Q) -O 


c 


00 












» •« 


«^ 








4J 




JS 


J= 


iH <U 


l-l CU 


3 














'-vj- -* 


-3- 








•H bO 


X 


bO 


bO 


CJ • 4J 




bO 
























S-< 


1 




00 CO 


vO 


00 


in 


CM 


r~ r-~ 


CM 


H 


o o o 


O 


•H -H 


bO 


3 


3 


CO /~\ 


o 


T3 




^ in 


00 


^ 


.—1 


<J^ 


O in 


CO 


Z 


r^ r-» <r 


^O 


CJ iH 


M 


^ 


^ 


<4-l l-l 14-1 


CO Cu 


tu 




00 in 


vD 


,—1 


vD 


CO 


CO CO 


CO 




CT^ in r-~ 


r>- 


CO X 


3 


CO 


CO 


0) O 


(U (U 


l-i 


t-«. 


* * 


•K 


^ 


* 


•« 


•K ^ 


•K 




»« •K * 


*> 


U-l Q) 


^ 


4J 


4-1 


- l-l 


.-H M 


0) 




■<!• -vi- 


-^ 


in 


in 


in 


so so 


so 




SO SO sO 


so 


O 


CO 


4J 


4J 


CO 3 


& 


T-t 




















tD U> so 


lO 


- ^1 
CO fn 


4-) 
4-1 


•H 


•H 
PU 


l-l 4-) CO 
<U CJ ^ 


a (u 
CO CO 
























>4-l 




















O O O 
C3N O ^ 


o 

CO 


U 
0) 


•H 

P-i 






P CO o 
3 <4-i O 


CO o 


y-i 




















CM in o- 


r^ 


U >, 




>% 


>, 


4-1 3 >H 


U 4J 


o 




















#. 0^ ffK 


«v 


3 Si 




^ 


^ 


O C U3 


<u 






vo O 


CO 


00 


in 


csl 


so 00 


CM 


H 


r- so ^ 


sO 


U 


>^ 






CO rt 


,£ c 


CO 


vO 


0\ r^ 

CM -H 


CO 
CM 


in 


in 

00 


o 


-vf ^ 

CM CM 


CO 


Z 


i^ so a> 


lO 


O t3 
CO (U 


^ 


CO 

C 


CO 


M-l a CU 

3 rH 


4J CO 
O X 


r^ 










•u 




*• ^ 


•K 


«K 


«• 


^ 


* ^ 


#1 




o o o 


O 


M-i a 


CO 


(U 


c 


c 4J a 


4J 


bO 




CO CO 


CO 


CO 


CO 


CO 


in >a- 


■<f 




in — < o 


in 


3 5 


C 


a 


(U 


CO o a 


l-l 


C 




















CO CM -* 


so 


c o 


Q) 


•H 


a 


e 3 CO 


< (U 


Q) 




















«s tfs tf^ 


•* 


CO 14-1 


a 


CJ 


•H 


13 CO 


M 




















•<}• in -* 


-3- 


a u 


•H 


0) 


CJ 


<U O 


& 


4J 




















so so sD 


lO 


0) 


O 


a 


(1) 


J2 l-l CM 


o 


CO 
























tu a. 


• <U 


CO 


a 


4-1 a. 


. iH 




























»— t .-H 


vO 


~a- 


in 


o 


o in 


00 


H 


H H H 


H 


j= 


i-i a 




CO 


a 


CO 


<u 




-t 00 


ON 


vO 


r^ 


CM 


rH <r 


p- 


Z 


Z Z Z 


Z 


■U CO 


1) CO 






4-1 O 


cu 4J 


> 


u-1 


o in 


r-^ 


<J- 


in 


in 


a> CM 


o 








CO 


M 


c 




CO 0) l-l 


XS CJ 


•H 




» ^ 


«K 


•K 


t^ 


•s 


•K VK 


#1 








JJ S 


3 


c 


C 


X <4-l 


3 O. 


CO 




CO CM 


CM 


CO 


CO 


CO 


CO -vj- 


<3- 








CO 


4J C 

o c 






T3 0) 


CJ 

in 


CO 


























Q) 




p^ <t 


vO 


r-v 


CM 


o 


00 CM 


in 


H 


H H H 


H 


bO 


CO >, 




hJ 


<U >% M 


0) .-1 


l-i 




o o 


O 


\o 


O^ 


CO 


in ON 


CM 


Z 


z z z 


Z 


•O C 


•4-1 hJ 






4J ^ CO 


l-l 


D. 


<J- 


CO r^ 


m 


o 


in 


00 


<r in 


o 








OJ -H 


3 


CU 




CO 


<U 0) 


Q 




w> #« 


*t 


^ 


•K 


•K 


«K as 


*^ 








4J 4J 


C 


^ 


0) 


u •« 


s XI 


o 




vO vO 


vO 


r-. 


^ 


vX3 


r-s so 


r~ 








CO CO 


CO <u 


CO 


J^ 


4J cu \o 




U 
























t-i (U 


e ^ 


hJ 


CO 


CO -o 


VO >^ 




























r~. r-< 


CJN 


H 


H 


9—1 


O -H 


^H 


o 


o o o 


o 


4-1 4-1 


CO 




i-J 


c c 0) 


1 CO 


1 




<r r^ 


o 


Z 


Z 


^ 


—1 CTn 


o 


■4- 


CM CM CM 


in 


CO 


>%kJ 






O 3 rH 


CM a 






in CM 


a^ 








00 <j> 


<JN 


CM 


o vo in 


o 


C bO 


J3 


<4^ 




a '4-1 a 




• 


ro 


f ^ 


«^ 








^ »» 


#1 


•• 


^ ^ #v 


«> 


o c 




o 


14-4 


<u s.' a 


r^ ^-s 


CT\ 




r~~ 00 


r— 








^H ^H 


^H 


O 


in in <r 


in 


a -H 


T) <W 




o 


T) CO 


Q) 3 
















r-i >—* 


1-H 


-H 


t— I t— t f-H 


rH 


<i> u 


(U o 






CO 


4J CO 


W 




















I/) in in 


J1 


"O (U 


4-1 


CO 




(U >. 


o <u 


hJ 
























<u 


CO 


4-1 


CO 


l-l U t-i 


C M 
























5 




00 r-v 


00 


H 


^ 


H 


r^ o 


-* 


o 


O O O 


o 


(U (3 


(U CO 


iH 


4-) 


cu o o 


3 




vO 00 


CM 


Z 


^ 


Z 


CM 00 


m 


f-H 


00 -H r^ 


CM 


M -H 


3 4J 


3 


iH 


!3 4-1 <4-l 


4-1 pq 


H 




vD a^ 


CO 








C3^ r^ 


00 


-* 


in ^ CM 


CO 


4) bO 


CTiH 


CO 


3 


CO 


O ^^ 




csi 


«^ ^ 


•^ 








^ ^ 


•k 


«t 


^ ^ *. 


*« 


> C 


Q) 3 


(1) 


CO 


t-^ U CO 


o 






CO <d- 


-* 








r-- r- 


r^ 


CJ\ 


CM CM CM 

J- J- J- 


CM 


I-H 
. i 


H CO 

CO 1-1 

CO 


4J 
CO 


(U 

)-l 

4J 


and 

Labo 

suit 


H-l CO 

CO 4J • 
Q) bO vO 


























• 1 • • 






in CO 


-* 


H 


H 


H 


O 0^ 


o 


o 


o o o 


O 


•^ -H <U ^~» 


4J • 


<u • 


CO • 


(U 


iH C vO 






CT. -H 


in 


Z 


Z 


Z 


in CM 


ON 


CM 


CO CO CM 


sO 


0) -H > to 


T) CO ^-s 


4J /-s 


(U ^-s 


so bO l-l 


a (U t 




-^ 


vO 00 


r^ 








CO o 


1—4 


-* 


in r^ -H 


■<r 


4J -H M 


0) (U (-1 


M 


4J M 


c 


a l-l vo 






•K A 


•» 








^ * 


»k 


* 


«^ #^ #^ 


•^ 


CO CO 4-1 a> 


4.1 4.) 0) 


OJ 


(U 


CO -H (U 


CO 4J O 






-* -* 


•^ 








sO so 


so 


SO 


p-> r* r-~ 
J- J- J- 


-T 


0) 4-1 (0 l-l 

4-1 O +J 3 


CO M 

(U 3 


t-i 
>^ 3 


>-l 

>. 3 


4J 4-1 ^ 

O CO H • 


c« M in 
1 


















3 rt 4-1 


•U P"-, 4J 


CO 4J 


CO 4-1 


3 CU >. 


1 <U M 






• • • 


CO 


• • 


CO • • 


CO 


• • • • 


4J T3 (U CJ 


CO o 


T3 CJ 


T3 O 


•OH CO 


• > CJ 




(U 


CO • • 


Ss 


• • 


>^ • • 


CO 


CO . . > 


O O CO (0 


4J TS CO 


1 CO 


1 CO 


O • T3 


W -H <3 




iH 


>% • > 


(0 


• > 


ct) . > 


>% 


V-i 4J O o ■< 


Z 1-1 oj y-i 


O 1 <*-! 


~3- 14-4 


in in 


l-l J3 CO 


H CO 




a. 


n o < 


T3 


o < 


'V O < 


CO 


<U CO Q Q 


a< u 3 


Z 00 3 


-3- 3 


-3- 3 


Pj bo QJ a) 


O CO T3 




a 


T3 a 




a 


a 


•a 


X 0) 


-H D. CcvJ oo C 


J- c 


IT) C 


3 3 rt 


Z (U M 




(« 




•* 




00 




4J W 


H 0) CO 


CO 


CO 


CO 


M CO 




M 


r* 




•— 1 






CM 




00 


O 




z Ma 


a 


a 


a 


ja o CO 


a-T3 



37 



Where specimen fracture occurred within 
the middle third of the span length, the 
flexural strength or modulus of rupture 
(R) was calculated as follows: 



Pi? 
bd^ 



where R = modulus of rupture, psi, 

P = maximum applied load, lb, 

i = span length, in, 

b = average width of specimen, 
in, 

and d = average depth of specimen, 
in. 



in the mine, and removed from the forms 
the following day. All of the samples 
analyzed by the private testing labora- 
tories were sawn. Initially only 28-day 
tests were to be performed; however, some 
measure of the early flexural capacity 

was considered necessary. Table 10 pro- 
vides the analysis results of the flex- 
ural strength testing. Since many of the 
test specimens were somewhat laminated, 
the lowest values were deleted and the 
highest two values are presented and 
averaged. Owing to the high incidence of 
laminations and the absence of any speci- 
men capping or grinding (shims were used 
as discussed in ASTM C 42-77), the over- 
all Bureau analyses results were lower 
than those obtained from private testing 
laboratories. 



The most serious problem encounterd in 
the testing was in obtaining a competent 
specimen. Laminations were present in 
the bulk, of the specimens. 

The initial Bureau-tested specimens 
were sawn out of large blocks with a 
diamond-tipped blade (fig. 36). Cutting 
time for the numerous specimens became 
excessive, however, and shot panels with 
suitable dimensions were later used. The 
gunite was shot directly into the pre- 
oiled forms and then trowelled to a 
smooth surface on top. The specimens 
were covered with plastic, left overnight 




FIGURE 36. - Diamond-tipped saw used to cut 
steel-fibered gunite specimens. 



Three different 24- by 24-in steel- 
fibered-gunite test panels of the same 
prebagged mix shot by the same nozzle man 
using the same gun on the same day and 
tested by the same independent testing 
laboratory gave flexural strength results 
that varied by as much as 640 psi (lowest 
to highest). As shown in table 10, for 
sample 6 the value for two of the sawn 
beams was almost 70 pet lower than the 
highest value. Out of a group of three 
beams sawn and tested from each of three 
shot sample blocks , one group had a mean 
of 1,006 psi, a second had 1,023 psi, and 
a third had 1,541 psi. This wide con- 
trast in flexural strengths of the sam- 
ples becomes even more cogent when it 
is realized that many of the products 
achieved lower flexural strengths (maxi- 
mum) than the observed variance of this 
product (even though their compositions 
were distinctly similar). 

This extreme range of analysis vari- 
ability is difficult to explain and can 
only be attributed to nozzle and gun crew 
operation and gun operation. Although an 
extremely high quality prebagged gunite 
mix can be purchased to remedy a spe- 
cific underground problem, one of the 
predominant factors in obtaining the 
high-strength finished product rests with 
the application of the product by the 
gunning crew. 



38 







«NJ \0 


a^ 


H 


H 


H 


v£> CM 


<r 


ir* iri tr^ 


H 


1 


0) 




4-1 


4-1 


4-1 1 (U •> 




r~^ 


CO vO 


ON 


z 


Z 


Z 


in CO 


<f 


z z z 


Z 


a j= 




U 


O 


to 43 V( O 




r—t 


CO O 


1—) 








^ CO 


CM 






o 


4-> 




3 


3 


O CU CT^ 




i—t 


•> r. 


•> 








^ ^ 


9^ 






o 






13 


-3 


13 !5 O 






^-< i-H 


^H 








1—1 i-H 


1-H 






IH 


,£3 




O 


O 


CU 43 


























4J 4-1 4-1 I-H 






CVJ O 


1— 1 


H 


H 


H 


in r^ 


1-H 


H i-^ f-f 


H 


(U 






CX 


CX 


CD bO CO 




vO 


r^ CO 


in 


z 


Z 


Z 


CO CM 


CO 


Z Z Z 


Z 


S 


•O 








<U 3 43 




.—1 


i-H i-H 


f— 1 








CO r^ 


in 






>. 


0) 








4J cu 4J •• 




^H 


•V *s 


«^ 








«S «K 


^ 






.H 


t3 




<U 


CU 


P CO 






^H 1—1 


^H 








1-H 1-H 


^H 






O 


C 




43 


43 


13 4-1 4-1 15 
3 CO O O 
























O^ 


3 




4-t 


4-1 






Cvj O 


i-H 


H 


H 


H 


in vt 


o 


ir> fr* i-t 


H 




MH 








«0 3 tH 




m 


CTi CO 


v£) 


Z 


Z 


Z 


r^ O 


CJN 


z z z 


Z 


X 


s.^ 




>. 


>. 


iH 13 iH 




r-H 


^ C^ 


O 








O -H 


o 






cu 






^ 


,Q 


CO O O 




^H 


^ 


^ 








#1 #t 


^ 






4-) 










•- M (J 14-1 






i-H 


1—1 








1-H 1-H 


1-H 






CO 






13 


13 


M 3 CX 
O i< CO 


























^ 




r-^ in 


^D 


H 


H 


H 


r^ v£) 


CM 


trt i-^ h^ 


H 




O 




CU 


CU 


43 CU <U CO 


o 


-Cf 


i-H CO 


CNI 


Z 


Z 


Z 


vo in 


vT) 


z z z 


Z 


CO 


4-1 




13 


T3 


4J iH 


fi 


1—1 


o o 


o 








1 — 1 1-H 


1-H 








CO 




3 


3 


3 iw CO •> 


•H 


.-H 


». ^ 


" 








•^ ^ 


•- 






tJ 


M 




3 


3 


CO CO ^O 






f— t i-H 


1-H 








1-H 1-H 


1-H 






d 


O 




14H 


IH 


>". 


0) 






















CO 


43 
CO 




bO 


bO 


cu CO cu (U 


J-i 






















43 -3 43 r-t 


CO 




V^ i-H 


■<r 


H 


H 


H 


00 -H 


in 


i-* irf H 


H 


>H 


hJ 




3 


3 


4-1 1 4-t CX 


3 


CO 


CM <!■ 


CO 


Z 


Z 


Z 


00 O 


<3- 


Z Z Z 


Z 


o 






•rl 


•H 


00 g^ 


cr 


1—1 


<r cvj 


CO 








in r^ 


v£) 






^ 


bO 




^ 


4-1 


>,CM UH CO 


CO 


^H 


.. •> 


•> 








•s .S 


^ 






4-> 


(3 




CO 


CD 


,Q O CO 


u 




1—1 ^H 


-H 








1-H 1-H 


1-H 






3 
CO 


•H 
4-1 




CU 
4J 


CU 
4J 


-3 VJ CO p 
























Q) 




cNi r^ 


o 


H 


H 


H 


ON -* 


1^ 


H H H 


H 




CO 




^^ 


•^-^ 


CU O 4«! O 


a. 




r^ cx) 


CTi 


Z 


Z 


Z 




00 
00 


z z z 


Z 


CU 

,i2 


0) 








4J l+H O <4H 
CO O 


CO 


r-H 












^ 








*-> 






>. 


>^ 


•H CU iH -3 


t3 














1-H 








>. 


(3 




iH 

o 


u 
o 


CD JJ 43 CU 


c 






















CD CO 3 


3 




ON — ^ 


in 


H 


H 


H 


ON r->. 


00 


H H H 


H 


iC 


o 




4J 


4-t 


CO 0) 'H 


O 


1—1 


CO i-H 


CM 


Z 


Z 


Z 


00 00 


00 


z z z 


Z 




CD 




to 


CO 


to iH to 


Ou 


i-H 


CM (NJ 


CM 








CO CO 


CO 






13 


4-1 




u 


U 


4-1 {X 4-1 




r— 1 


.. •> 


•> 








^ ». 


•- 






CU 


M 




o 


^ 


- CO 43 


»■ 




1-H I-H 


f— 1 








I-H .-H 


1-H 






4-) 


0) 




43 


o 


CD Q CO O 


CO 






















CD 

•H 


43 

q 




to 

h-3 


to 


<U CD 


C 






















•H O 


cu 




m v£> 


o 


<f 


^H 


CO 


CM r^ 


o 


H H H 


H 


CD 


Pi 








4J • CM CO 





o 


00 00 


00 


00 


■<f 


vO 


r-- <l- 


1-H 


z z z 


Z 


CO 






bO 


bO 


•H r-N r-l 


•H 


1— ( 


in in 


in 


■o- 


O 


in 


o in 


vD 






to 


c« 




d 


3 


rH ^1 CO 


o 




























•H 


•H 


•H CU O 






















cu 




-H ^H 


i-H 


CM 


CO 


00 


CM rH 


CM 


H H H 


H 


r. 


bO 




4J 


4-t 


U M M cu 


a- 


c^ 


-H i-H 


^ 


r^ 


00 


C^J 


Csl O 


1-H 


z z z 


Z 


CO 


C 




CO 


CO 


CO 3 MH JH 


CO 




vo in 


in 


<r 


in 


in 


vO ^O 


^ 






(U 


•H 




(U 
H 


^ 


MH 4-1 (U 
O (U !3 


























cu 




H H 


H 


H 


H 


H 


H H 


H 


H H H 


H 


4-) 


43 








- CO »H 


4-1 


00 


2: iz 


3 


z 


Z 


Z 


Z Z 


Z 


\z z :z 


Z 


•H 


(U 








CO IH CO CO 


•H 




CM Csl 


CM 


CT) 


CO 


oo 


tr) CO 


CO 






rH 


o 




^ 


42 


M 3 cu 


c 






















•H 
O 






bO 
U 


bO 


cu 3 ^ CO 


3 














~^ 








»^ eg >, 


bO 






9- 


CJN 


r^ 


CO 


00 C3N 


ON 


o o o 


CO 


CO 






3 


3 


3 cu ^ 






^-s /-s 


<l 


ON 


<f 


CM 


<3N in 


r^ 


St VO -H 


o 


M-l 


>. 




X> 


43 


4J iH CO 


-d 


r-^ 


CM Csl 


Z 


-* 


CO 


<r 


in in 


in 


C3N 00 CT. 


ON 




43 




CO 


CD 


o 4-1 a 3 


cu 




^^ v-^ 














U) O) 1^ 


1^ 


CD 


13 




4-> 
4-» 


4-t 
4J 


to O to 
MH 3 to 
























0) 


















in o o 


1-H 


JH 


9i 




•H 


•H 


3 13 CD M 


^ 


















o in r^ 


-* 


(U 


e 




Ph 


Ci^ 


3 O CU 


•H 


















in in in 


in 


>H 


>H 


• 






5 >H M 43 


M-l 


















,— 1 ^H 1-H 


1-H 


3 

4J 


O 


M 
CU 


43 


^ 


CX O 4-1 

14H O 


1+-I 




/-\ /-^ 


cx 


o 


p^ 


<y\ 


in CM 


C3N 


l£) l^ to 


li> 


O 


»H 


^J 






cu cu 


O 


vD 


Csl Osl 


<c 


in 


o 


r^ 


ON <r 


1-H 






to 


<U 


3 






43 43 CO (U 










v-^ x.^ 


» 


■^ 


in 


<f 


<f in 


in 


in in o 


vO 


<4H 


CX 


4-) 


CO 


CD 


4-1 4-1 4-1 (1) 


^ 


















CO in CO 


O 


3 




o 


3 


3 


rH H 


4-1 


















O O C3N 


o 


C 


CO 


CO 


9i 


9i 


4-1 3 jC 

CO >% CO H 


tkO 


















^ «s 


^ 




to 


KH 








c 


















^H r-H 


1-H 


^ 


I? 


3 


•H 


•H 


43 (U 


(U 


















U3 LO U> 


ID 






3 


O 


O 


p 


u 






















CU 


bO 


1 


CU 

CX 


CU 

CX 


13 -3 • 


4J 






















(U 0) CU >% 


CO 




00 O 


vj- 


o 


t^ 


ON 


00 CO 


v£> 


H H H 


H 


. 4-) 


C 




CD 


CD 


4-t xt ,3 to 
CO 3 H -3 






<!• O 


r-^ 


^H 


^ 


CO 


00 CM 


o 


z z z 


Z 


X) 


•H 


>. 






rH 


in 


r-^ o 


vO 


00 


vD 


r^ 


t^ o 


ON 






CU 4-> 


4-) 


^ 


3 


3 


Vj 3 


to 














^ 








4J CO 


CD 




3 


3 


4-1 MH cu 
















1-H 








CD 

CU T3 


CU 
4.) 


T3 
0) 






CD ^^ • 
3 CD CO 


P 






















53 




0\ 00 


-* 


^o 


CTi 


00 


C3N \Ci 


00 


^ ^ ^ 


H 


4J <U 




4-) 






O >^ CD 


CU 


<r 


in CM 


<y\ 


CM 


v£) 


-* 


r-. r^ 


CM 


z z z 


Z 


4J 


bO 


CD 


(U 


CU 


M CO 


iH 




in -vT 


<d- 


■vJ- 


<f 


vt 


in -vi- 


in 






4-) CO 


(3 


CU 


^ 


4«5 


<u o (U cu 


fe 






















O U 


•H 


3 


CO 


to 


13 4-1 JD ^ 


























in a, 


a. 








<t ON 


CM 


o o o 


o 


Z 4J 


M 


cr hJ 


)J 


CO 4-1 


1 




vi- <: 


<ti 


H 


H 


H 


CO <t 


<f 


i-H ^O CO 


CO 


CD 


CU 


cu 






O 5h 3 






C3^ Z 


2 


z 


Z 


Z 


o o 


O 


CM 00 O 


o 


c 


CU 


M 






CD O 'H MH 


• 


CO 












#v r^ 


^ 


*^ #« ^ 


^ 


H O 


(3 




<4H 


MH 


rH 43 1 O 


o 














I-H 1-H 


1-H 


CM ^ CM 


CM 


Z 6 


•H 


CO 


O 


O 


CO CO CM 


.— 1 


















in un un 


LO 


cu 

13 


bO 


CO 


CO 
4-t 


CD 
4-t 


1-3 —1 CD 
CU CU 


w 






















M bO >> 


^ 




^ a 


a 


H 


H 


H 


r^ CO 


in 


O O O 


o 


. (U 


^■*\ 


cu 


iH 


iH 


<U 3 43 .rH 


^ 




<!■ < 


<J 


Z 


Z 


Z 


00 CM 


in 


^ m in 


CM 


(U V-i 


CD 


4-) 


3 


3 


;? 'H 4-t 


fvj 


r~- Z 


z 








vO 00 


r^ 


r^ r^ v£) 


r^ 


rH CU 


• U 


CD 


CO 


CD 


4-1 1 


H 


















1-H 1-H 1-H 
J- J- J- 


1-H 
J- 


CO 
•H —1 


tlve 
ture 


(U 
4-) 

4-1 


cu 


(U 


r^ CD CO 4-1 

cu 3 
13 H >. cu 
3 X> U 




























ON a, 


a 


H 


H 


H 


eg O 


I-H 


o o o 


o 


.H 1 


to o 


O 


■p 


4-1 


CO cu • 






CN <J 


<d 


Z 


Z 


Z 


^ o 


00 


00 CO CM 


1-H 


D^ "— ' 


4-t to . 


3 


CD • 


CD • 


43 1 MH O 




-H 


m z 


z 








o r>. 


vO 


•^ -St CO 

«v ^ ^ 

^H I-H ^H 


1-H 


CX -H 

to 

CO 


3 iw cu 

CU 3 rH 

CD 3 Pu 


CD 

3 


CU /-v 

4-1 h 

CU 


4-1 M 


o bo CO MH in 

P -HO 

CD 3 -3 " 


















J- ^ J- 


J- 


4.) 4J 

o o 

Z 3 


<u 2 d 
M a CO 

CX CO 


•H 


(H 

>. 3 

CO 4-1 


>^ 3 

CO 4-1 


4-J 43 O — • 
O CD >-l CM 
















3 4J MH -3 






CO • • 


CO 


• • 


CO • • 


• • • • 


13 


(U 4-) 


CJ 


-3 O 


t3 O 


13 4-1 4-13 




0) 


>^ • > 


>. 


• > 


>N • > 


CO • • > 


O 


M o ts 


CU 


1 CO 


I to 


O -H -3 CO CO 




rH 


CO . <d 


CO 


• <« 


CO • <: 


)H 4J • • < 


CX (H 


3 CO 


a-<r ^w 


in <4H 


(H Ph (U 




D. 


TS O 


-r* 


O 


•tS O 


0) CD O O 


< Oj 


>. TJ P3 


zn 


•<t 3 


<r 3 


CL, 3 4J •> 




d 


Q 




Q 


Q 


42 <U Q Q 


z- 


3 OcM 


-o J- 3 


^ 3 


^ <U -H O O 




CO 


r^ 


<d- 




00 


4-t -U 


CO M 




tO 


cO 


43 CO 43 CO 




C/3 






--H 






CM 




O 


1 




CX CX 










4-1 4-t CO ON 



39 



Although the flexural strength test, as 
used in this paper, can be used with 
considerable success in determining the 
quality of fibered gunite, the Flexural 
Toughness Index may soon supplement the 
flexure test and take its place in the 
quality control and testing of fibered 
gunite and concrete. This engineering 
property is essentially a measure of the 
specimen's ability to sustain additional 
loading after the first crack occurs 
(when the matrix of the gunite or con- 
crete has failed) , when the stress-strain 
curve moves through the ultimate strength 
and continued additional loading is sup- 
ported by the interlocking nature of 
the cemented fibers only. Although re- 
searchers have attemped to quantify this 
load-bearing capability, the parameter 
is not at present usable in any design 
procedure. 

The toughness index was calculated for 
some fibered specimens in this study. As 
shown in figure 37 for one of the tested 
specimens, the (proposed) toughness in- 
dex is calculated as the area under the 



3,500 


1 


1 1 1 






First-crack 


f^ — Ultimate strength 




3,000 


- strength / 


\ 


- 


2,500 


/ 


\ 0.075- in 


- 


^ 2,000 


/ 


\ deflection 


- 


o 1,500 


- / 


V 


- 


1,000 


- / 


\i 


- 


500 
n 


' 1 


1 1 ! 1 1 


^ 



0.02 0.04 0.06 0.08 0.10 0.12 
DEFLECTION (FLEXURAL), 0.02 in/in 

FIGURE 37. - Flexural strength curve of a 
steel-fibered gunite sample. 

load-deflection (L-D) curve out to 0.075 
in, divided by the area under the load 
deflection curve of the fibrous beam up 
to the first-crack strength (proportional 
limit defined as the first deviation from 
linear) (29) : 



Toughness index = 



area under L-D curve to 0.075 in deflection , 
area under L-D curve to first crack 



The toughness index, however, is not 
standardized as it should be. One source 
defines the term as "the area under 
the load deflection curve out to 0.10 in 
(2.54 mm), divided by the area under 
the load-deflection curve of the fi- 
brous beam up to the first crack strength 
(30)." When more precisely defined, the 



parameter will measure the amount of work 
required to strip the fibers in the fail- 
ure crack plane from the concrete ( 31 ) . 
Owing to the controversy involving this 
engineering parameter (see appendix F) , 
the toughness index data are not herein 
presented. 



POROSITY AND PERMEABILITY ANALYSES 



Fibered-gunite products are subjected 
to relatively harsh moisture conditions 
when applied in deep coal mine environ- 
ments. The exposed gunite surface is in 
constant contact with mine ventilation 
air that in some instances exhibits rela- 
tive humidity conditions that may ap- 
proach 100 pet. Unless mine ventilation 
air is dehumidified, primarily during 
the hot summer months , the mine atmos- 
phere can resemble a dense fog. Addi- 
tionally, when fibered gunite is used for 
roof and rib support in deep mines (metal 



or nonmetal) containing high-sulfur ores 
or in high-sulfur coal seams (sulfur con- 
tent exceeding 1,5 pet), the gunite may 
be subjected to seepage or drainage that 
is moderately to highly acidic. The 
drainage contacts the outer and inner 
surfaces of the gunite (where the gunite 
contacts the coal or rock surface) and 
causes deterioration of the alkaline ce- 
ment structure. This causes loss of ad- 
hesion, strength, and sealant protection 
of the host rock surface. 



40 



The hydraulic conductivity (permeabil- 
ity) and porosity of the fibered gunite 
determine the rate of seepage migration 
through the material from the rock-gunite 
contact surface outward, and are also 
directly related to the propensity for 
absorption of acidic drainage or vapor 
inwardly. Gunite permeability and/or po- 
rosity, therefore, may be one of the 
primary factors in determining the dura- 
bility of the material, which involves 
primarily its alkali-acid reactivity, 
leaching characteristics, resistance to 
chloride or sulfate attack (and the sub- 
sequent expansion and cracking) , rein- 
forcement steel corrosion, and freeze- 
thaw characteristics. 

For the above reasons, it was consid- 
ered pertinent that this investigation 
include porosity and/or permeability 
analyses of the tested gunite samples. 
The analyses were performed by the author 
at the Department of Energy's Bartles- 
ville Energy Technology Center in Bar- 
tlesville, OK. Owing to the suspected 
presence of extremely low permeability 
readings (in the 1 x 10~^ darcy range) , a 
special research apparatus and technique 
were developed for the permeability anal- 
ysis phase of this investigation. 

The gunite samples were cored with pre- 
cision equipment to an outside diameter 
of 1.5 in and a length of 2.75 in. Both 
ends of the cores were trimmed with a 
precision laboratory diamond- tipped core 
saw. Although great care was used in 
coring and trimming the gunite samples , 
the laminated zones (especially in the 



steel-f ibered samples) caused some core 
dimension irregularities. Some specimens 
had to be shortened somewhat to remove 
laminated zones. 

The gunite porosity analyses were de- 
rived by the following procedure: 

1, The cores were dried in a constant 
temperature oven at 115° for 24 h. 

2, Core dry weight and length dimen- 
sions were recorded. 

3, Bulk volume was caluclated using 
the formula 

bulk volume = irr^j^, 

where r = radius of core 



and 



I = core length. 



4. The cores were then placed in a 
vacuum cell, which was evacuated and then 
submerged in water under a high vac- 
uum for a minimum of 4 h. Figure 38 
shows the laboratory setup for sample 
evacuation. 

5. The cores were then removed from 
the water, blotted, and weighed. The 
weight of the saturated water (saturated 
core weight minus dry core weight) and 
volume of the saturated water (weight of 
the saturated water divided by density of 
the water) were then calculated. 

6. Porosity of the samples was then 
determined by the formula 



Porosity i<^) = 



weight of the saturated water 
density of the water 



irr^Jl 



41 



This method of extracting a sample po- 
rosity value is an offshoot of the true 
formula: 

(<!)) pet = ^ • 100 



or (j) pet = ^^j ^s . 100, 



where 



and 



Vt 
Vp = pore volume, 

Vt = total volume, 

Vc = solid volume. 



The porosity value obtained by this meth- 
odology may be more appropriately known 
as the effective porosity in that it re- 
lates directly to the volume of intercon- 
nected pores and their ability to uptake 
water under vacuum. 

Table 11 summarizes the porosity data 
acquired for the samples. The complete 
data file is presented in appendix C. 
Porosity measurements are, at best, dif- 
ficult to acquire and prone to error. 
Although error in porosity analyses is 
inversely proportional to the total sam- 
ple volume (thus the sample should be 




FIGURE 38. - Gunite core air evacuation sys- 
tem for porosity analysis. 

large) , the samples were considered to be 
large enough to permit reasonably short 
evacuation times without inducing skin- 
effect aberrations in the porosity data, 
caused by incomplete filling of the in- 
nermost pores by the brine (water). The 
absorption of water along the length of 
the fiberglass strands (in those samples 
containing fiberglass) may have induced 
error that increased effective porosity. 



TABLE 11, - Gunite density and porosity 



Sample 


Core density, 


Core porosity, 


Sample 


Core density. 


Core porosity. 




g/cm^ 


pet 




g/cm^ 


pet 


1 


2.01 


25.59 


10 


2.18 


18.62 


2 


2.10 


20.41 


11 


2.16 


19.25 


3 


2,11 


17.45 


12 


2.16 


19.56 


4 


2.12 


19.98 


13 


2.13 


20.62 


5 


1.69 


34.95 


14 


0) 


0) 


6 


2.00 


25.09 


15 


1.96 


29.78 


7 


2.01 


24.49 


16 


2.06 


21.60 


8 


1.81 


29.67 


17 


1.96 


210.10 


9 


2.10 


20.90 









^Defective sample. 

2a major portion of this 



lamination zones. These samples con- 



porosity is in the 
tained styrene butadiene latex polymer. 
NOTES. ~ 

1. Although steel-f ibered specimens are normally considered to have a homogeneous 
distribution of the fibers, concentrations were found in lamination zones, possibly 
inducing density errors. 

2, Samples 5 and 8 are f ibered surface bonding mortars (cements) and therefore 
contain larger pore volumes and interconnected pores. 



42 



It should be noted that samples 15-17 
contained sytrene butadiene latex poly- 
mer. Although they exhibited low compar- 
ative porosity readings, they would have 
had even lower porosity values had they 
not contained minor lamination zones. 

Fibered-gunite permeability analyses 
were conducted using the laboratory setup 
diagrammed in figure 39 and shown in fig- 
ure 40. The procedure involved the con- 
finement of a previously evacuated, satu- 
rated section of core in a precisely fit- 
ting rubber sleeve within a stainless 
steel Hassler tube. The core was flooded 
under pressure with a metered amount of 
fluid. As shown in figure 41, the core 
is fitted with fluid gathering and in- 
jecting Teflon endpieces of the same 
diameter as the core; these have inlet 
and outlet orifices. The endpieces are 



locked in place by brass endcaps. The 
rubber sleeve around the core is sealed 
and heavily pressurized to a minimum of 
100 psig above the metered flow pressure 
of the core flooding pump to prevent lat- 
eral skin flow along the core exterior 
length. Any fluid collected at the out- 
let end of the Hassler tube, therefore, 
was measured and considered to have moved 
through the core matrix. 

Owing to the extremely low permeabili- 
ties of the gunite core samples, a capil- 
lary tube was used to collect the core 
flood water at the outlet orifice. Water 
column height increase over a monitored 
period of time was used to calculate the 
permeability characteristics. 

The following conditions were main- 
tained for the research: 




Cheminert double-plunger 
metering pump with variable 
flow rate 



Metering valve 
Water delivery gauge 



Methylene blue 
indicator solution 



Rubber tubing 



Pump air valve 
supply line 



High-pressure fluid in 



High-pressure .. ^ . 
pump (180 psig) ^^J^"^ 




yZn\ scale 

l/16-in-l D 
flowmeter tube 



Metering 
valve 



{13 



Fluid out 

(atmospheric 

pressure) 




Teflon cap plug 



Stainless steel 



^V^ Core confining ^ ,, , , . j 
^ ^ pressure (fluid) ^^^sler tube and caps 

(in cross section) 



High-pressure gauge 



Bypass 



Note= Not to scale. 
Hassler tube expanded 
to show detail 



FIGURE 39. - Gunite permeability analysis system diagram. 



43 




FIGURE 40t » Gunite permeability analysis equipment. 



1. The laboratory and water temper- 
ature was maintained constant at 22° 
to 23°C. A water viscosity of 0.94 cP 
(32) was used in all the permeability 
calculations. 

2. Hassler tube outer sleeve pressure 
(for core confinement) was maintained at 
a constant pressure of 180±5 psig. 

3. Hassler tube core inlet pressure 
was maintained at a precise 80±5 psig 
setting, using a precision metering 
value. 

4. A precision Cheminert metering pump 
with variable flow rates was used to in- 
ject and flood the confined gunite cores 
with water. A 100-yL/min flow rate (Q) 
was selected and used throughout the re- 
search effort. 

5. Air pressure used to control the 
Cheminert metering pump piston valves was 
maintained at a constant 60 psig. 

6. New methylene blue indicator solu- 
tion was injected into the capillary out- 
let riser tube to allow precise visual 
readings . 




FIGURE 41. - Hassler tube and associated core 
permeability measuring apparatus. 

The permeability of the somewhat porous 
gunite medium is a measure of its ca- 
pacity to transmit fluids or, more suc- 
cinctly defined, a measure of the fluid 
conductivity of the material. The perme- 
ability represents the reciprocal of the 
resistance the porous medium offers to 
fluid flow (33) . The practical unit of 
measure of permeability is the darcy and 
its submultiples , the millidarcy (10~^ 
darcy) and microdarcy (10~^ darcy). Dar- 
cy 's law, expressed with fluid viscosity 
parameters, made it possible to define 
penffeability when it was determined that 
a thin slice of material, in this in- 
stance a core of gunite, with thickness 
dx and cross section S, is traversed per- 
pendicularly at its faces by a rate of 
flow Q (counted in volume at the tempera- 
ture and average pressure of the slice) 
of a fluid with viscosity y, and is af- 
fected by a pressure differential, dp. A 
generalized form of Darcy 's law applies 
here and is written as follows: 



dp=Max 



Sk dp 

or Q = — • -r*^ 

^ M dx 



7. Capillary cross-sectional area was 
determined to be 0.0198 cm^ by using the 
formula Tir^, where radius is 1/2 the in- 
side capillary diameter (1/16 in). Cap- 
illary length of water accumulated over a 
unit time provided volume per unit time. 



°^ ^ s • d? 



with the coefficient K 
permeability (34) . 



being the 



44 



TABLE 12. - Gunite mean permeability values 



Sample 


Permeability, 
10"^ darcy 


Std dev, 
10"^ darcy 


Sample 


Permeability, 
10"^ darcy 


std dev, 
10"^ darcy 


1 


4.14 

29.75 

2.12 

15.02 

168.89 

122.27 

62.87 

8.34 

15.74 


0.86 

1.42 

.68 

.54 

2.88 

1.78 

3.74 

.45 

.60 


10 

11 

12 


13.92 
11.61 
3.31 
5.36 
0) 
<1.0 
<1.0 
<1.0 


0.20 


2 

3 


.67 
.64 


4 


13 


.79 


5 


14 


0) 


6 

7 


15 

16 


NA 
NA 


8 


17 


NA 


9 





NA Not available. 
^Defective sample. 
NOTES.— 

1. Laminations effectively shortened the core length, making the permeability val- 
ues larger than normal in cores with such laminations. 

2. Samples 15-17 were styrene-butadiene-latex- impregnated gunite cores and were 
determined to be essentially impermeable to fluid movement. 

3. Although the compressibility of water may be a factor here and varies with 
pressure, temperature, and dissolved gases, the factor was disregarded in the perme- 
ability calculations. 



For this investigation, the permeabil- 
ity analyses were determined using a for- 
mula that was extracted and simplified 
from the Darcy 's law equation since Q, 
dp, y, and S were maintained constant. 
The extracted equation used to calculate 
permeability in this research was as 
follows: 

Vt y 



K = 



A AP 



Owing to the sensitivity of the system 
and to the extremely low permeabilities, 
at least six timed runs were performed on 
each sample. The data accumulated are 
presented in appendix D, Table 12 shows 
the mean (arithmetic average) values and 
standard deviations, calculated using the 
formula 

(Ix)2 



I 



x 



2 _ 



Sx = 



n 



n-1 



where V = volume of fluid collected in 
the capillary, cm^ , 

t = time, s, 

M = water viscosity, cP, 

A = core cross-sectional area, 
cm^, 

AP = pressure differential across 
the core (inlet-outlet) , 
psia, 



Since permeability and porosity are di- 
rectly related in some types of materi- 
als, an effort was made to determine the 
relationship of the two factors for the 
gunite samples. The porosity and perme- 
ability data were compared using a linear 
regression computer program to best fit a 
straight line to the plotted data points. 
Porosity values were plotted on the ab- 
scissa (x axis), and permeability values 
were plotted on the ordinate (y axis). 
The general linear regression formula 
used in the curve fit (straight line) 
calculation was 



and 



L = core length, cm. 



45 



b = 



a = 



r2 = 



LxiYi 



!.xi 



ly, 



n 



2 _ 






yi 



- b 



n 



•Xi 



LxiYi - 



Ix, I 



yi 



(Ixi)2 , 
Ix,^-— -—Ix.^- 



dx,)^ 



o 
o 

T3 
CD 
'O 



UJ 



160 



120 



80 - 



CD 

< 40 

UJ 







1 
A 


1 


1 ' 1 ' 


- 


+ 


y^ 


- 


+ >^ 


^ " 


•X 


1 


. +, , , 



n 



20 



24 



28 



32 



36 



Figure 42^4 is a curve fit of the 
porosity-permeability data of gunite 
specimens 3-10 plus 12 and 13. Figure 
42B shows the same data minus specimen 8, 
which was a surface-bonding cement and 
caused an errant relationship and line 
fitting. R-square, the correlation coef- 
ficient of the two parameters, was 0,569 
in plot A and 0.885 in plot S. Correla- 
tion coefficients that approach 1.0 indi- 
cate excellent data correlation. 

The range scale of the x-axis was 
shifted to the right in plot A to expand 
the cluster of data that occurred to the 
right of the abscissa-ordinate intersect 
point. The right-lateral shift in poros- 
ity data and consequent negative ordinate 
intercept is an indication that a portion 
of the porosity present (lamination 
zones, air pockets, etc.) is not avail- 
able for fluid flow (permeability). The 
plots indicate a good correlation between 
the gunite porosity and permeability data 
for the samples compared. 

The lowest observed permeabilities oc- 
curred in the latex polymer gunite sam- 
ples. The high-strength silica fume wet- 
mix gunite was second with a permeability 
of just over 2.0 x 10~^ darcy. One seal- 
ant (surface bonding cement) material 
(sample 5) exhibited an extremely high 
penneability compared to the normal gun- 
ite specimmens. 



o 

O 

■o 
to 
'O 



>- 

_J 

m 
< 

LU 

QL 
LU 
Q. 




5 10 15 20 25 30 35 
POROSITY, pet 

FIGURE 42. - Linear regression curve fit of 
porosity and permeability. 



The gunite specimens exhibited a gen- 
eral trend of increasing permeability 
with decreasing compressive strength. 
Permeability also tended to increase with 
an increase in water-cement ratio, al- 
though enough specific water-cement ratio 
data were not available to confirm the 
trend. Fiber type did not appear to 
directly affect permeability. Sample 
laminations, particularly in the steel- 
fibered specimens, masked any potential 
correlations of fiber type and content 
with permeability. 



DELIVERY HOSE STATIC DISCHARGE 



During the application of two dry-mix 
f iberglass-fibered-gunite products, con- 
tinuous, strong, 1-1/2- to 2-in-long 



blue-white static discharges were ob- 
served along the delivery hose. Although 
the discharges were primarily observed 



46 



to take place between the hose and the 
slightly damp concrete mine floor, one 
nozzle operator stated that he sometimes 
felt a shock. Although the occurrence of 
the discharges in the Lake Lynn Exper- 
imental Mine was not dangerous , in an 
operating deep coal mine with methane and 
coal dust in the mine air and blasting 
materials in common use, such static dis- 
charges may be extremely dangerous, par- 
ticularly in return airways or nonven- 
tilated areas. The minimum ignition 
potential of methane-air mixtures occurs 
at 0.9 of stoichiometric mix (which is 
9.48 pet methane in air) and requires 
less than 0.5 mj of energy (35) . The 
discharge of 10 mJ capacitive energy 
through a bridgewire is enough to fire an 
electric blasting cap (36) . The concen- 
trated discharge of static from the dry 
mix delivery hose to a pointed conductive 
metal object may, therefore, be suffi- 
cient, under the right circumstances, to 
ignite methane or to fire an electric 
blasting cap. 

The relative humidity in the mine at 
the time of the static discharge observa- 
tion was 44 pet, and the temperature of 



the mine air was 49° F. The combination 
of the dry, cold air with the relatively 
dry concrete mine floor may seldom be 
duplicated in an operating coal mine, but 
the possibility does exist. The relative 
humidity readings taken during the re- 
mainder of the dry-mix-type gunite appli- 
cations ranged from 48 to 57 pet, and 
static discharges were not observed. The 
wet-mix gunite application had no ob- 
servable static discharges, as would be 
expected. 

The development and use of a sheathed 
(metallic) mesh discharge grounding sys- 
tem for delivery hoses would add consid- 
erable bulk and weight to the hose and 
would make it unwieldy and difficult to 
clean. The solution to static bleed off, 
therefore, may rest in the impregnation 
of better conductive fiber or metallic 
strands in the hose wall itself. Al- 
though many delivery and placement hose 
types are designed to be "static dissi- 
pating," the observed static discharges 
are proof enough that the hazard poten- 
tial remains, particularly during dry, 
cold (low relative humidity) seasons. 



GUNITE OPERATION CREW REQUIREMENTS 



One of the most important factors in 
the application of fibered gunite is the 
selection, training, and on-the-job ex- 
perience of the gunning crew. Most crews 
consist of three or four members: a 



nozzle operator, a gun operator, and one 
or two gun loaders . One of the crew 
serves as the foreman and must be thor- 
oughly familiar with all facets of the 
operation including equipment setup and 





TABLE 


13. - Gunite crew requirements 






Sample 


Type of mix 


Nozzle and hose 


Gunite gun 


Hopper 
loaders 


Other 


Crew total 


1-3 

4-5 


Wet 
Dry 
Dry 
Dry 
Dry 


1 

1 

32 

32 

1 


2 
1 


1 
1 


13 
2 

^2 
2 
2 


2l 






63 


7 
4 


6-8 


4 


9-10 

11-17 


55 
7 



^The wet-mix method required a concrete-mortar mixer crew of 3. The manufacturer 
had not established a prebag mix at the time of the application demonstration. 
^1 crew member sprayed curing compound on the freshly applied gunite. 
3l crew member operated the nozzle and/or water valve and 1 assisted with the hose 



movement. 

4 



The hopper loaders also performed gun adjustments. 
^A 6th person, identified as a sales representative, assisted to a limited degree. 
^Samples 11-17 were demonstrated at the manufacturer's facilites 



the author. 3 additional crew members were present, 
tlons, but mainly assisting in latex polymer pumping. 



accompanied by 
performing a variety of func- 



47 



operation, water and air pressure and 
volume adjustments for optimum gunning 
conditions, and rock surface preparation, 
scaling, and washdown requirements. Ta- 
ble 13 provides a comparative breakdown 
of the gunite crews used by the various 
manufacturers of the products tested. 
Each gunite manufacturer that partici- 
pated in the comparative application re- 
search was urged to bring its most exper- 
ienced, seasoned gunite crew. 

Gunite shot rate ranged from 1,350 
Ib/h for a surface-bonding cement shot 
with a special gun to 9,491 Ib/h for a 
f iberglass-fibered dry-mix gunite (table 
14) . Most of the gunning rates averaged 
approximately 6,000 Ib/h (1.5 yd^/h as- 
suming gunite weighs 4,000 Ib/yd^). The 
in-place application rate, considering 
water added, gun losses, etc., ranges 
from 1.1 to 2.9 yd^/h for the dry-mix 
gunite. Sealant and surface bonding ce- 
ment rates were less. Shooting rate for 
the wet-mix gunite was estimated at 0.38 
yd^/h, but the wet-mix gun is rated at up 
to 7.8 yd^/h. Owing to the crews' pre- 
cise measuring of the ingredients and 



additives, the wet-mix gun's capacity was 
not remotely approached. 

Some gunite manufacturers do not main- 
tain a complete mobile crew to perform 
gunite training and demonstrations for 
their specific product. During the ap- 
plication of one product, three different 
men from one crew were permitted to run 
the nozzle, two apparently for the first 
time. One of the three operators had the 
water valve setting so open the wet gun- 
ite ran down the mine rib. A second 
operator later sprayed dry dusty gunite 
material on the top of the wet zone, ap- 
parently to dry it up. 

The company that applied products 9 and 
10 maintains a trained crew for use in 
teaching coal company crews the correct 
method of applying their products. One 
piece of equipment that permitted this 
crew's close coordination and precise ad- 
justment of the gunite gun and nozzle was 
a voice-activated (permissible in coal 
mines) communication headset-microphone 
system, worn by the nozzleman and gun 
operator. Air and water pressures. 



TABLE 14. - Gunite shooting rate 



Sample 



Shot 
duration. 



mm 



Bags 
shot 



Bag 

weight, 

lb 



Total 

gunite 

weight , lb 



Gunite shot 



bags/min 



Ib/h 



1 



ydVh' 



3 (wet-mix) 

4 

4^^ 

55 

6 

7 

8 

9 

10 (roof)... 
10 (rib) 



167 
83 

125 
60 
70 
38 
40 
55 
50 
52 



NA 

180 

170 

27 

128 

64 

48 

145 

67 

75 



NA 
50 
50 
50 
60 
60 
50 
60 
80 
80 



34,200 
9,000 
8,500 
1,350 
7,680 
3,840 
2,400 
8,700 
5,360 
6,000 



NA 
2.25 
1.36 
.45 
1.83 
1.68 
1.20 
2.64 
1.34 
1.44 



1,509 
6,506 
4,080 
1,350 
6,583 
6,063 
3,600 
9,491 
6,432 
6,923 



0.38 
1.73 
1.10 

.36 
1.61 
1.52 

.83 
2.95 
1.73 
1.87 



NA Not available. 

•"^For shot durations of less than 1 h, rate is shown assuming the same rate would 
have continued for 1 h. 

^Assumes a cubic yard weighs 4,000 lb and contains 3,700 lb solids and 300 lb wa- 
ter. This figure considers specimen collection and gun losses (not rebound) and rep- 
resents cubic yards in place. 

^This is a rough estimate provided by the manufacturer. The low gunning rate was 
due to the precise additive blending and gunite characteristics measuring before 
shooting was allowed. 

'^Sample 4 was shot during 2 monitored periods of time. 

^Surface bonding cement. 



48 



gunite feed rate, rotor speed, and nozzle 
distance were varied In synchronous tim- 
ing as the nozzle operator moved from rib 
to roof application areas and maintained 
constant verbal contact with the gun 
operator. The results of the verbally 
communicated coordination of movement in- 
clude a reduction in rebound waste (hence 
lower costs) , better compaction of the 
finished product (hence higher strength) , 
and a more uniformly applied product. 

Several points made by two of the par- 
ticipating manufacturers who had given 
training sessions to gunite equipment and 
product purchasing clients in the mining 
industry include — 

1. Only the long-term, responsible 
personnel of the company should be given 
the gunite training and then only if 
those personnel are to function as a gun- 
ite crew on a regular basis. The manu- 
facturers found that in many instances 



when they returned to a mine (at the mine 
superintendent's request) no more than 6 
months after a full-scale training ses- 
sion, the gunite crew contained none of 
the originally trained personnel, 

2. Equipment used to convey and pneu- 
matically apply fibered gunite products 
is subjected to severe internal abrasion 
and must have the specified maintenance 
performed if it is to function properly. 
A gunite gun capable of applying gunite 
with no more than 10 to 15 pet rebound is 
quickly converted into a 50-pct waste 
generator when poorly maintained and im- 
properly operated. Inefficient gunning 
techniques and the attendant high costs 
cause mine management to forego the ob- 
vious safety benefits obtainable from 
f ibered-gunite products. An adhered-to 
training policy and equipment maintenance 
schedule will reduce a high percentage of 
the gunite costs that are attributable to 
waste rebound. 



GUNITE COST ANALYSIS 



The ultimate cost per cubic yard of in- 
stalled fibered-gunite products depends 
on a number of factors: 

A, Cost of the gunite materials (prebag 

or bulk) : 

1. Cement content and type. 

2. Fiber content and type. 

3. Other ingredient proportions (ag- 

gregates, sand, etc.). 

4. Special additives in the mix 

(e.g., silica fume, fly ash, 
ground slag) . 

B, Products required in applying the 

gunite: 

1. Accelerators. 

2. Plasticizers and/or water re- 

ducers (wet-mix) . 

3. Superplasticizers (wet-mix). 



4. Specialty additives (e.g., sty- 
rene butadiene polymer), 

6. Curing compounds. 

C. Application crew requirements. 

D. Application equipment. 

E. Rebound percentage (waste) and gun 

dust losses. 

Tables 15-17 provide an analysis of the 
generalized costs of some of the categor- 
ized items. Materials costs vary geo- 
graphically; therefore, the costs pre- 
sented reflect a general Northeast U.S. 
average. 

The general price quoted for bulk gun- 
ite sand and aggregate if of a river sand 
variety is $13/ton to $15/ton, according 
to a major producer. Gunite manufac- 
turers with their own dredging operation 
or located near one may pay as little as 
$7/ ton to $8/ ton for river sand. Manu- 
factured sand or sand-sized limestone 



49 



TABLE 15. - Portland cement price data^ 



Type cement 


Bag price 
(per 94 lb) 


Bulk tanker price 
(per 1,000 lb) 


Cost per yd 3 
(in gunite)^ 


I 


$4.22 
4.36 
4.52 


$60.00 
63.00 
66.00 


$45.00-$59.00 


II 


47.25- 61.43 


Ill 


49.50- 64.35 



^Prices were quoted for June 1983 by a major cement 
producer. 

^Gunite cement content ranged from approximately 750 to 
974 lb/yd3. 



TABLE 16. - Gunite fiber price data 



Fiber type 


Cost per Ib^ 


Concentration , ^ 
lb/yd3 


Cost per yd^ 
(in gunite) 


Steel 


$0.30 

1.80 

.90 

5.00 


350-265 
^40 
^+40 
M.6 


$15.00-$79.50 


AR-f iberglass 

E— fiberglass 


72.00 
36.00 


Polypropylene 


8.00 



^Price data approximated for April 1983 by a gunite manufacturer. 

^These figures represent the concentration of fibers normally 
used in gunite products. The figures do not imply that equivalent 
performance will be achieved by the various fiber types at these 
concentrations . 

^50 Ib/yd^ represents approximately 0.4 pet by volume, and 265 
Ib/yd^ represents approximately 2 pet by volume (7^). The precise 
volume percentage varies slightly with fiber configuration. 

^Average. 



TABLE 17. - Wet-mix gunite admixture costs 



Material 



Drum price^ 
per gal 



Bulk price^ 
per gal 



Dosage, 
oz/100 lb 
cement 



Cost per yd^ 
(in gunite)"^ 



Accelerator (liquid) 

Accelerator (liquid) (nonchloride) 
Plasticizer and/or water reducers: 

Hydroxylated carboxylic acis,... 

Lignosulf onates 

Polymer admixture 

Superplasticizers : 

Sulfonated naphthalene formalde- 
hyde condensate 

Sulfonated melamine formaldehyde 
condensate 



$5.00 
19.50 

5.50 
3.75 
7.25 



8.50 
6.00 



$2.50 
17.50 

NA 
2.00 
4.50 



5.50 
3.00 



16-64 

NA 

2- 4 
6-10 

3- 9 



10-20 
24-40 



$2.30-$12.18 

NA 

.64- 1.68 
.70- 1.52 
.79- 3.08 



3.22- 8.37 
4.21- 9.14 



NA Not available. 

^The prices and additive rates were provided by a major concrete and cement product 
supplier. 

^Drum price based on a 55-gal quantity. 

3 Bulk price based on 5,000-gal quantity minimum. 

'^Gunite cement content ranged from 750 to 975 Ib/yd^. The cost in gunite range is 
based on the bulk price if available. 



50 



aggregate, such as was contained in sev- 
eral of the tested products, can also be 
purchased for $7/ton to $8/ton or slight- 
ly less if the manufacturing facility is 
located near an operating quarry. 

The cost of the styrene butadiene latex 
polymer additive used in gunite samples 
15-17 ranges from $6.35/gal in 1- to 10- 
drum (55-gal) quantities to $4.18/gal in 
a 3,000-gal tank car. At a nominal mix- 
ture rate of 3-1/2 gal per bag of cement, 
a 9-bag/yd^ gunite mix would require 31.5 
gal at a cost of $132/yd3 to $200/yd3 
of gunite (depending on the quantity of 
chemical purchased) . This price informa- 
tion was obtained from a major producer. 

The prebagged, dry-mix fibered gunite 
contains all of the necessary ingredients 
for application except water. Curing 
agents were not used for any dry-mix 
product tested in this investigation. 
Prices on a per-bag basis ranged from 
$3.05 per 50-lb bag to $4.25 per 60-lb 
bag for f iberglass-f ibered gunite. Sur- 
face bonding mortars (containing high 
concentrations of portland cement) cost 
$4.69 to $6.95 per 50-lb bag. Steel- 
fibered prebagged dry-mix gunite cost 
from $3.49 per 60-lb bag to $3.80 per 
80-lb bag. Cost per cubic yard through 
the gun ranged from $226 to $262 for 
f iberglass-fibered gunite (by weight) 
and from $176 to $258 for steel-f ibered 
gunite (by weight) . The f iberglass- 
fibered surface bonding mortars (ce- 
ments) , of which only two were tested, 
cost $347/yd3 to 514/yd^ (by weight) . 
The products were pneumatically applied 
for demonstration purposes only. The 
polypropylene-f ibered gunite (only one 
tested) costs $157/yd^ through the gun. 
Appendix E presents the complete cost 
data for the dry-mix products involved in 
this investigation. 

The wet-mix gunite applied in the Lake 
Lynn Laboratory Mine contained the con- 
ventional cement, aggregate, fibers, and 
water plus an accelerator, plasticizer, 
water reducer, superplasticizer, and sil- 
ica fume additives. A curing compound 
was also used. Specific quantity amounts 
of the various admixture ingredients used 



in the three wet-mix products were not 
revealed by the manufacturer. All par- 
ticipating gunite manufacturers, however, 
signed an agreement with the Bureau that 
any contained additives would not be 
flammable or impart gaseous vapors or by- 
products that would be noxious or dele- 
terious to human health upon exposure to 
moist mine environments and/or explosive 
research such as will be conducted in the 
area where the gunite products were ap- 
plied. Some of the additives were mea- 
sured out precisely in graduated cylin- 
ders and added to the gunite batch mix- 
ture. The wet-mix admixture work for 
specimens 1-3 was performed by a graduate 
research engineer with the company that 
manufactures the wet-mix gunite gun. 
This particular wet-mix recipe, there- 
fore, required highly specialized techni- 
cal personnel. 

The manufacturer of the wet-mix gunite 
products provided a range of materials 
content for the products. Documentation 
provided by the company indicated that 
plasticizer, superplastizer , and acceler- 
ators were added, but volumes were not 
specified. A cost estimate for the wet- 
mix, steel-f ibered, silica fume gunite 
was prepared in order to provide cost 
comparison with the prebagged dry-mix 
products. Table 18 presents the esti- 
mated data derived for specimen type 3 
from various sources. The estimated cost 
of $235/yd3 to $323/yd3 through the gun 
does not include curing compound cost, 
equipment charges, or labor. The wet-mix 
high-strength silica fume gunite is ex- 
pected to cost $300/yd3 to 310/yd3. Cost 
per cubic yard would be less for wet-mix 
specimen types 1 and 2, which are of low- 
er strength. 

Table 19 presents a prebagged cost (es- 
timate) comparison of dry-mix and wet-mix 
gunites (as tested) . The estimated com- 
parison is provided with the assumption 
that some liquid additives (other than 
water) may be required. Based on an ex- 
pected cost of $300/yd3 to $310/yd3, the 
type 3 steel-f ibered gunite could cost 
$134/yd^ (through the gun) more than 
the lower priced steel-f ibered dry-mix 
gunite. The decreased rebound of the 



51 



TABLE 18. - Cost estimate for prebagged, wet-mix, silica fume, steel-f ibered gunite 



Material 



Quantity 



Cost (bulk) 



Cost per yd- 



Cement (Type III) 
Sand (aggregates) 
Fibers (imported) 
Silica fume 



Accelerator •'^ 

Plasticizer^ 

Superplasticizer^ . 

Total materials. 
Other cost items :^ 
Sealable paper 
bags. 
Overhead costs^... 

Total 

Profit^ 

Total cost (est) 

through- the-gun . 
Expected cost 



890 to 950 Ib/yd^. 

2,400 Ib/yd^ (est) 

150 lb/yd3 (est). 

15 to 18 pet (by 
wt) of cement. 

16 to 64 oz/100 lb 
of cement . 

4 to 8 oz/100 lb 

of cement. 
10 to 20 oz/100 lb 

of cement . 
NAp 

46 to 74/yd3 



$66/1000 lb 

$13/ton to $15/ton. 

$0.50/lb (est) 

$50/ton to $75/ton. 



NAp. 
NAp, 
NAp. 
NAp. 

NAp. 



$5/gal 

$2/gal to 3.75/gal 

$3/gal to 5.50/gal 

NAp 

$0.15 to $ 0.20 each... 
$0.50/bag to $ 0.70/bag 



$59 -$63 (est) 
16 - 18 

75 (est) 
3.50- 6.75 (est) 

5.80- 11.90 (est) 

1.01- 2.14 

2.13- 8.36 



NAp. 
NAp. 

NAp. 



162 


-185 


6. 


90- 14.80 


23 


- 52 


191 


-252 


44 


- 71 



235 



300 



-323 



-310 



NAp Not applicable. 

•'•Type or quantity of accelerator was not revealed by manufacturer. Cost estimate 
derived by assuming dose rate of 16 to 64 oz per 100 lb cement, cement content of 890 
to 950 Ib/yd^, and cost of $5/gal. 

^Type or quantity of plasticizer was not revealed by the participating manufac- 
turer. Cost estimate was derived by assuming a dose rate of 4 to 8 oz per 100 lb ce- 
ment, cement content of 890 to 950 Ib/yd^ , and cost of $3.75/gal. 

^Type or quantity of superplasticizer was not revealed by the participating manu- 
facturer. Cost estimate was derived by assuming a dose rate of 10 to 20 oz per 100 
lb of cement, cement content of 890 to 950 Ib/yd^ , and cost of $3/gal to $5/gal. 

^To compare prebagged wet-mix and dry-mix products, the bag cost, overhead cost and 
profit must be estimated and included. 

^This range is provided based on information provided by one of the participating 
dry-mix gunite manufacturers, using a profit range of 23 to 28 pet. 

TABLE 19. - Prebagged gunite cost comparison 



Type 


Fiber 


Compressive strength 
as tested, psi 


Cost per yd^ 
(by weight) 


Dry-mix. . . 
Wet— mix. . . 


Steel 


^9,668 
^,700 
27,000 
^7,637 
^12,000 
^5,000 


$176 

258 

226 

157 

^$300-310 


Fiberglass 

Polypropylene. . 
Steel 









^Private laboratory. ^Bureau of Mines. 

^Based on a statement from the manufacturer, the cost per 
cubic yard for the silica fume high-strength wet-mix gunite may 
approach $300 to $310. Note that some of the wet-mix additives 
may not have dry (nonliquid) substitutes and, accordingly, 
could not be prebagged. 



52 



wet-mix gunlte, compared to that of the 
dry-mix types, would reduce this cost 
differential by up to 5 to 8 pet. The 
increased strength of the tested wet-mix 



gunite over that of dry-mix types may 
also require less thickness (hence lower 
volume) to provide the same structural 
support on a given gunite job. 



CONCLUSIONS AND RECOMMENDATIONS 



Gunite Engineering 
Parameter Relationships 

Strength differences exhibited by fi- 
bered and nonfibered gunites in com- 
pression were obvious but not dramatic. 
Strength differences between fibered and 
nonfibered gunites in flexure, however, 
were dramatic. The differences were sig- 
nificant enough to conclude that for ap- 
plications (e.g., mining) where prospec- 
tive differential loading is possible and 
flexural movement may occur, some type of 
fiber must always be used when guniting. 



The highest strength 
contained steel fibers. 



gunite products 



Wet-mix, steel-f ibered gunite with sil- 
ica fume and an array of admixtures 
showed the highest compressive and flex- 
ural strengths of the gunite products 
tested. 

When dry-mix steel-f ibered gunites are 
sprayed in multiple-layered applications, 
lenses of poorly cemented material (lami- 
nations) develop. Uniaxial compressive 
and flexural failure occurred at the lam- 
ination lenses repeatedly. Laminations 
were also found in the fiberglass-f ibered 
products. 

Polypropylene-fibered samples (specimen 
13) had higher 7- and 28-day compres- 
sive and flexural strengths than AR- 
fiberglass-f ibered samples (specimen 14) 
which were of similar composition, shot 
through the same gun by the same noz- 
zleman, and tested at the same private 
laboratory. 

Specimens gunned outside in daylight 
had flexural and compressive strengths 
of higher value than identical products 
gunned in the diminished light of a min- 
ing environment. The strength increases 
obtained significantly exceeded the 



15-pct difference between cored and cubed 
sample strength (products demonstrated 
outside were tested at private labora- 
tories and cubed samples were taken) . 

Gunite permeability tends to increase 
as compressive strength decreases and as 
the water-cement ratio increases. Gunite 
fiber content did not appear to affect 
the permeability of the material. 

Splitting tensile strength analyses are 
not an applicable test procedure for fi- 
bered (especially steel-f ibered) gunite 
poured cylinders , if specimen rodding is 
performed in the test cylinder to induce 
compaction. The isotropic orientation of 
the fibers is disrupted, preferred lon- 
gitudinal orientation occurs and a sub- 
sequent reduction in splitting tensile 
strength results. 

Gunning Techniques and Rebound 

Gunite sample blocks shot by the same 
nozzleman using the same prebagged mix, 
the same gun, the same day, and tested by 
the same laboratory gave sawn beam flex- 
ural strength variations of almost 70 
pet, indicating that the gunning tech- 
nique has a dominating effect on the 
final product strength. 

The application of wet-mix gunite, as 
used and tested in this investigation, 
required a highly trained technician to 
perform admixture addition. Serious in- 
teracting physicochemical reactions can 
occur if the additives are not introduced 
to the gunite in the correct amounts and 
in consideration of their synergistic 
effects. 

Although only an estimated rebound was 
obtainable for the wet-mix products in 
this investigation, this rebound was the 
lowest of all gunite types tested. 



53 



The mean rebound (excluding the highest 
and lowest values) for the dry-mix gunite 
tested was over 20 pet. A rebound value 
of less than 16 to 18 pet is extremely 
difficult to achieve and can only be ob- 
tained by the most proficient of gunning 
crews . 

A major portion of the rebound col- 
lected for the steel-f ibered products was 
steel fibers and larger sized aggregate 
particles. Although other factors may 
have more effect, the shorter f ibered 
(steel) gunite had lower rebound. 

The use of steel fibers, particularly 
in the dry-mix equipment , appears to in- 
duce pulsation activity in the gun, re- 
sulting in a higher propensity for lami- 
nations. Laminations were present in all 
of the cores taken from dry-mix steel- 
f ibered specimens. 

The maintenance of dry-mix guns is cri- 
tical in mines with high ventilation air- 
flow rates; otherwise serious product 
strength reduction may occur from cemen- 
titious fines separation. 

Air pressure fine tuning and nozzle- 
rock surface distance adjustment are as 
important as water flow rate adjustments 
when moving from rib to roof application 
with dry-mix gunites. 

For dry-mix applications, reduced air 
pressure with a closer (24 to 30 in) 
nozzle-to-roof distance appeared to re- 
duce nozzle spurting and loss from the 
peripheral edges of the spray pat- 
tern (hence reduced rebound) , The re- 
duced air pressure also cuts dust, per- 
haps at the expense of compaction (and 
ultimate strength) . 

After approximately an hour of constant 
gunning, the nozzle operators were ob- 
served to experience considerable arm 
fatigue. The roof -nozzle angle of appli- 
cation and distance began to change ac- 
cordingly, resulting in higher rebound. 

The gunning rate of the wet-mix gunite 
applied in this investigation was slower 
than that of any dry-mix type except one 



surface-bonding cement. The slow appli- 
cation rate was due primarily to the pre- 
cise batch mixing of the ingredients and 
admixtures . 

Gunite Dust 



The wet-mix high-strength gunite had 
a higher total dust loading in milli- 
grams per pound shot than four other 
gunned dry-mix products. The dust was 
primarily generated at the mixer. 

Four out of eight of the dry-mix gunite 
dust loadings would have exceeded the 
standards for dust if the operation had 
continued for a full shift or if the gun- 
ning was being done near a working sec- 
tion that was generating high dust 
levels . 

Gunite dust loading is almost entirely 
a function of crew performance methods 
and gun condition. 

A direct correlation was observed be- 
tween dust generated at the gun and re- 
bound. In all but one case (gun malfunc- 
tion) , high dust at the gun gave high 
rebound. 

Gunite Safety 

Fiberglass fibers, as well as steel 
fibers, can penetrate cloth gloves 
and clothing and cause abrasions and 
skin irritation when the gunned products 
are handled. Fiberglass allergies are 
documented and can cause minor 
discomforts. 

Steel fibers are dangerous when being 
gunned, since they travel at high ve- 
locity and have considerable penetra- 
tion power. When gunning on hard rock 
surfaces , the fibers have an initial high 
rebound percentage and can inflict seri- 
ous eye damage unless protective glasses, 
or preferably goggles, are used. 

Gunite Cost 

Silica fume appears to be a more cost 
effective way of obtaining lower perme- 
ability, higher strength gunite than 



54 



using latex polymers. Other, untested 
characteristics, however, may justify the 
use of polymer gunite in specialty appli- 
cations underground, 

Through-the-gun cost for steel-f ibered 
dry-mix gunites tested is $176/yd^ to 
$258/yd^ (by weight) compared with $300/ 
yd^ to $310/yd^ (expected cost) for wet- 
mix, high-strength, silica fume, steel- 
f ibered gunite, excluding labor. Reduced 
rebound and shot thickness requirements 
for the wet-mix gunite may offset a por- 
tion of the cost differential. The tech- 
nical admixture staff requirements of the 
wet-mix silica fume material may add to 
the cumulative installation costs. 

The cost comparison per cubic yard of 
the various fibered products tested 
revealed that the steel-f ibered dry- 
mix prebagged gunite is the least expen- 
sive and has the highest strength, 
when compared with other fibered dry-mix 
products. 

General Conclusions 

Bird-nest blockage of the gunite equip- 
ment, which was a serious disadvantage 
when attempting to hand -mix the fibers In 
conventional mixers, has been virtually 
eliminated by the prebagged mixes. The 
use of fibers with larger diameter (or 
equivalent diameter in the case of non- 
round fibers) and shorter lengths has 
reduced the problem even more. These 
factors and the recent trend toward fiber 
deformation (kinking, end enlargement, 
corrugating, etc.) have reduced the prob- 
lem to an insignificant level. 

Aggregate size fraction distribution is 
critically important in wet-mix gunites 
that employ silica fume. 

Recommendations 

Strong static discharges were observed 
along the gunite delivery hose during the 
application of two dry-mix products. The 
static discharges may be capable of ig- 
niting methane concentrations or of deto- 
nating blasting caps under ideal condi- 
tions. Better static discharge grounding 



or bleed-off is recommended for dry-mix 
gunite delivery hose systems if used in 
deep mine return airways and nonventi- 
lated areas. 

A nozzleman training and certification 
program would be of considerable benefit 
to the gunite industry and would help 
standardize the quality of the gunned 
material. 

The flexural toughness index parameter 
needs professional attention by the gun- 
ite industry to resolve the issues re- 
garding the influence of fiber length and 
first-crack strength on the index value. 
The engineering parameter would be useful 
in preparing specifications as well as 
in product quality control and strength 
testing. 

A gunite product-by-product standard 
strength factor may be beneficial. The 
factor could be prepared by obtain- 
ing flexural strength or toughness in- 
dex values from samples of material that 
had been precisely mixed, poured into a 
sized mold, vibration-compacted, cured to 
specification, and tested using a stan- 
dard procedure. The standard strength 
factor would represent a target strength 
for the gunning crew. Deviations from 
the standard strength factor would repre- 
sent the gun crew contribution to the 
product strength. The gunite products 
could be classified according to achiev- 
able strength, making product selection 
by the user less difficult when the mate- 
rial was needed for a particular purpose, 

Gunite application with a gun operated 
on compressed air in an underground mine 
is too loud to permit efficient verbal 
communication between the gun and nozzle 
operators. Low-rebound, high-quality ap- 
plication can only be accomplished wherv 
good communication is available — espe- 
cially when the nozzle operator is mov- 
ing from roof to rib. An MSHA-approved , 
voice-activated headset is highly recom- 
mended for use in mining gunite work. 

Even the wet-mix equipment used in this 
investigation with its sophisticated 
nozzle-operator remote control system 



55 



could have benefited from the use of a 
communication system. 

Careful observation of the operating 
dry -mix nozzles in the mine revealed that 
unless the nozzle end was held vertical 
(in roof shooting) blockage occurred on 
the tilted lower side, forming a roll of 
wet gunite that converged inward on the 
moving stream and then began pouring off 



onto the floor to become waste. Nozzle 
improvements , using a conical stream of 
air around the periphery of the orifice, 
may redirect the waste roll back into the 
main stream of material. The design sug- 
gested may require an additional hose and 
fitting for high-pressure air but would 
be beneficial, especially from a cost 
standpoint. 



REFEBIENCES 



1. American Concrete Institute. ACI 
Manual of Concrete Practice — 1980. Part 
V. Recommended Practice for Shotcreting 
(ACI 506-66). 1980, pp. 506-1 to 506-19. 

2. American Concrete Institute Com- 
mitte 506. State-of-the-Art Report on 
Fiber Reinforced Concrete. Dec. 3, 1982, 
pp. 1-43. 

3. Lankard, D. R. An Overview of 
Steel Fiber Reinforced Concrete (SFRC). 
Paper 1, Steel Fiber Reinforced Con- 
crete - A Review of the State-of-the-Art. 
Batelle Development Corp., May 1982, 
pp. 1-19. 

4. Poad, M. E,, M. 0. Serbousek, and 
J. Goris. Engineering Properties of 
Fiber-Reinforced and Polymer-Impregnated 
Shotcrete. BuMines RI 8001, 1975, 25 pp. 

5. American Concrete Institute. 
State-of-the-Art Report on Fiber Rein- 
forced Concrete reported by ACI Commit- 
tee 544. ACI Pub. 544.1R-82, May 1982, 
pp. 9-29. 

6. Prestressed Concrete Institute 
Journal. Prestressed Concrete Institute 
on Glass Fiber Reinforced Concrete Pan- 
els. Recommended Practice for Glass Fi- 
ber Reinforced Panels. V. 26, No. 1, 
Jan. -Feb. 1981, pp. 1-33. 

7. Woods, H. Corrosion of Embedded 
Materials Other Than Reinforcing Steel. 
Concrete and Concrete-Making Materi- 
als. ASTM Spec. Tech. Pub. 169-A, 19 
pp. 230-238. 



8. Roller, A. Fiber Reinforced Con- 
crete. Construction Specifier J., v. 35, 
Dec. 1982, pp. 44-55. 

9. Grutzcek, M. W. , S. Atkinson, and 
D. M. Ray. Mechanism of Hydration of 
Condensed Silica Fume in Calcium Hydrox- 
ide Solutions. Fly Ash, Silica Fume, 
Slag and Other Mineral By-Products in 
Concrete, Am. Concrete Inst. SP-79, 
1983, pp. 643-664. 

10. Bernhardt, C. J. SiO Fume as Ce- 
ment Addition. Betongen IDAG J, (Nor- 
way), v. 17, Apr, 1952, pp, 29-53. 

11. Jahren, P. Use of Silica Fume 
in Concrete. Fly Ash, Silica Fume, Slag 
and Other Mineral By-Products in Con- 
crete. Am, Concrete Inst, Pub, SP-79, 
1983, pp, 625-643, 

12. Regourd, M, , B, Mortureux, P, C, 
Aitcin, and P. Pinsonneault, Microstruc- 
ture of Field Concretes Containing Silica 
Fume. Paper in Proceedings of the 4th 
International Conference on Cement Micro- 
scopy, March 28-April 1, 1982, Las Vegas, 
Nevada, ed, by G, R, Gouda, Int. Cement 
Microscopy Assoc, Duncanville, TX, 1982, 
pp. 1-12. 

13. Fesil Silica. Tech. Bull., (Oslo, 
Norway). A. S. Fesil & Co. June 1980, 
1 p. 

14. Cement and Concrete Association 
Journal, A Report of a Joint Working 
Party of the Cement Admixture Association 
and the Cement and Concrete Association, 



56 



Superplasticizlng Admixtures in Concrete. 
1976, pp. 1-33. 

15. Malhotra, V. M. Superplasticiz- 
ers: Their Effect On Fresh and Hardened 
Concrete. Concrete Int. J, v. 3, No. 5, 
May 1981, pp. 66-81. 

16. Concrete Construction Journal. 
How Super Are Superplasticizers? V. 27, 
May 1982, pp. 409-415. 

17. Travis, R. B. Classification of 
Rocks. Q, CO Sch. Mines, v. 50, No. 1, 
Jan. 1955, p. 17. 

18. Price, W. H. Concrete Aggre- 
gates — Grading and Surface Area. Ch. in 
Concrete and Concrete-Making Materials. 
ASTM Spec. Tech. Publ. 169-A, 1966, 
pp. 404-413. 

19. Henager, C. H. The Technology and 
Uses of Fiberous Shotcrete — A State-of- 
the-Art Report. Battelle Development 
Corp., 1977, pp. 1-59. 

20. Ryan, T. F. Gunite, A Handbook 
for Engineers. Cement and Concrete As- 
soc, London, 1973, pp. 1-61. 

21. Hendricks, R. S. Shotcrete Gives 
Stronger Support at Lower Cost. Min. 
Eng., V. 22, May 1970, pp. 69-73. 

22. Breslin, J. A., and G. E. Niewia- 
domski. Improving Dust Control Technol- 
ogy for U.S. Mines. The Bureau of Mines 
Respirable Dust Research Program 1969-82. 
BuMines Impact Rept., 1982, 40 pp. 

23. U.S. Code of Federal Regulations. 
Title 30 — Mandatory Health Standards — 
Underground Coal Mines, Subchapter 0, 
Subpart B; Part 70 — Respirable Dust Stan- 
dard When Quartz Is Present; Jan. 1980, 
p. 423. 



24. 



Title 30 — Regulations and 



Standards Applicable to Metal and Nonmet- 
al Mining and Milling Operations. Sub- 
chapter N; Part 57 — Air Quality, Ventila- 
tion Radiation and Physical Agents; Jan. 
1980, p. 124. 



25. Liebhafsky, H. A., H. G. Pfeiffer, 
E. H. Wins low, and P. D. Zemay. X-Ray 
Absorption and Emission in Analytical 
Chemistry, Wiley, 1960, 357 pp. 

26. Malhotra, V. M. Contract Strength 
Requirements — Cores Versus In-Situ Evalu- 
ation. Am. Concrete Inst. J., Title 74- 
16, Apr. 1977, p. 167. 

27. American Society for Testing and 
Materials. Standard Test Method for Com- 
pressive Strength of Cylindrical Concrete 
Specimens. C 39-72 in 1977 Annual Book 
of ASTM Standards. Part 14: Concrete 
and Mineral Aggregates ; Manual of Con- 
crete Testing. Philadelphia, PA, 1977, 
pp. 25-28. 

28. Gonnerman, H. F. Effect of End 
Condition of Cylinder on Compressive 
Strength of Concrete. Proc. ASTM, v. 24, 
pt 2, 1924, pp. 1036-1065. 

29. American Concrete Institute Com- 
mittee 544. Measurement of Properties 
of Fiber Reinforced Concrete. Am. Con- 
crete Inst. J., Title 75-30, July 1978, 
pp. 283-289. 

30. Ramakrishnan, V., W. V. Coyle, 
L. J. Fowler, and E. K. Schrader. A Com- 
parative Evaluation of Fiber Shotcretes. 
Civil Eng. Dep. SD Sch. Mines and Tech- 
nol. Rep. SDSM&T-CBS 7902, Aug. 1979, 
p. 10. 

31. Lankard, D. R. The Engineering 
Properties of Steel Fiber Reinforced Con- 
crete. Paper 2. Steel Fiber Reinforced 
Concrete - A Review of the State-of-the- 
Art. Batelle Development Corp., May 
1982, pp. 1-31. 

32. Perry, J. H. , C. H. Chilton, S. D. 
Kirkpatrick, and D. Sidney. Chemical En- 
gineers Handbook. McGraw-Hill, 4th ed., 
1963, pp. 3-201. 

33. Amyx, J. W. , D. M. Bass, Jr., and 
R. L. Whiting. Petroleum Reservoir Engi- 
neering - Physical Properties. McGraw- 
Hill, 1960, pp. 64-129. 



57 



34. Monlcard, R. P. Properties of 
Reservoir Rocks; Core Analysis. Gulf 
Publ. Co., 1980, pp. 43-84. 

35. Litchfield, E, L. , T. A. Kuba- 
la, T. Schellinger, F. J. Perzak, and 
D. Burgess. Practical Ignition Problems 
Related to Intrinsic Safety in Mine 
Equipment. Four Short-Term Studies. Bu- 
Mines RI 8464, 1980, p. 4. 



36. Prugh, R. W. , and K. G. Rucker. 
Static Electricity Hazards in the Pneu- 
matic Loading of Blasting Agents. Paper 
in Proceedings 5th Symposium on Rock 
Mechanics (Univ. MN, May 1962), ed. by 
C. Fairhurst. Pergamon, 1963, pp. 419- 
438. 









PQ 


















Xi 

1-1 








CO d 
o 






(0 






















CO 1-1 






r-< 


■< t-~ <! -* CM 


o> 


00 vO CM VO 


o 








CO u 




w 


3 


Z ro a - 


"1 cs 


-* 


.-H ,-H CO ^H 


o 






• 


T-t 




tj 


S 








ii> 






CO 






4.1 


^-^ CO 




a 


P 














•o 






CJ 


d d 

O CO 




•* 


Pt, 














c 








•rl U 




•a 
















CO 






o 


u u 




















d 


<: 




















CM 


CO 1 




3 
























u u 




O 


Cfl 


<! vo < -<r — t 


CO 


00 m CM VD 


CO 






^ 


•H tu 




XI 


i-H 


!S CO Z - 


-t CNJ 


-* 


.-1 .-I CO — 1 


"O 






o 


r-l t4H 




1J 


3 








113 






•H 






CO 


CX 14H 




pi 


g 


in ro 
en ■-I 








r-t 

o 






O 


CX 3 
CO ,Q 






O 




J- 










CO 






Ot 








fc 














f\ 






CO 


CO (U 
4-1 . ^ 
•H CO 4J 




-o 
























c 


XI 


<! o < o O 


o 


o o o o 








>s 


CO 




3 


1-1 


Z in z in m 


0^ 


O O 00 CM 


o 






S 


d <u d 




o 




in o c» 


O 


m c^ 00 o 


o 






6 


•H r-l •H 




,i2 


#> 




». 


#s 


#> 




^ ^ » ^ 


1^ 








bO 




01 


4-1 


fO -H 


.-H 


r-H f— 4 1-H f— t 


■s 






*> 


T5 d 




« 


S 














CO 






u 


CU •H -O 

CO d (U 


























< r~ < <r 00 


in 


o -* in 00 


CO 






o 


3 CO W 






m 


Z ^ Z ^O 00 


vO 


— 1 0^ CO vO 


c 






<4H 


(U u 






Xi 


r^ in CM 


^H 


00 -H <t -* 


1-1 






0) 


>i B <u 






r-t 












•■ 


CO 






IH 


r-l r-l 




4-) 














^H 


4-1 






<u 


rH - rH 




O 
















c 






^ 


CO CU O 




















X! 




< o < — 1 en 


o 


00 <3" 00 ^ 


o 






*J 


U O 




CO 




Z 00 Z C3N m 
^ 00 <r 


m 


O 00 <5^ <d- 

o <■ m vD 


o 






#> 


u o 

O 14H 4-1 




p 






». 




LO 




^ fK 


•a 






•T3 


d tu o 




(U 


CvJ 


t-H 






<-t rH 


C 






d 


u d 




4-1 


XI 


1 












CO 






s 


4J OJ 




cfl 


1-t 


m 
















o 


o ,d CO 




3 




^ 










X3 

1-1 






XI 
0) 


d w rt 
v.^ 3 










« 
















p 


•* 








t-H 










O 








(u -a 




















O 






<u 


*j iH d 






























<1 0\ vO 00 v£) 


in 


O 00 -* CM 


O 






3 


d CO 3 




u 


>> 


>— ' 


Z fO CO 00 CJ> 


in 


r-. CT\ -* vO 








u 


tu o 




2 


PQ 


4-1 




• ■ 


• • 


• 




• • • • 


<r 






H 


S 00 x> 




CO 




s 


CM ^ 




CM CO ^ rt 










p. (U 
iH CU pi 




































< 00 O 00 -< 


vO 


00 ON CO vO 


CO 






• 


3 rH 




ro 




<-H 


Z CM m in CO 


r-~ 


t^ O vD r-- 


x: 


• 




4-1 


cr cu 




T3 


>. 


1-1 




• • 




• 




• • ■ • 


bO 


O 




o 


0) B 




>-l 


m 


o 


CO CM ^ 




CM ~a- ^ -H 


•H 


-* 




Cl- 


CO u 


< 






> 














0) 








CJ tn . o 


H 




















3 


o 




in 


•H to 4-1 




















< 


m 






<C 


CO CO 




CO CO ■* vt 










4-1 iH d o 


a 


•a 






z 


-*- 


^ "^^ 




•^ 


^ *^^ ^^ ^^ 


tr) 


14H 




o • 


to O C5 tu 




>^ 




•—* 




OJ CSJ 




CM CM -H ^ 


-d 


O 




4J XI 


S >4H -rl CO 


o 




>. 


4-1 




1 


1 




1 


1 1 1 


>% 






r-^ 


3 4J 


^ 


M 


m 


S 


-* -* — 1 ^ 


-* 


.— » i—i ^Si \0 




O 




CO 


tu to CO d 


s 


(U 






1^ t^ \0 vO 


i-~ 


vo ^o ^r -* 


t-H 


•H 




o 


d 4J CJ o 


o 


a 


















CO 


4-1 
CO 


4-1 


^- 


a. to •H ti 


pa 


















T3 rH 4J 


g 


to 




■-H 
















u 


O 


U 


x: a CO 


bO 


>. 


1-1 


■< -* ■-* m in 


<r 


m m -H -H 


« 




x: 


3 <U 


4-1 Tj a. p 




CO 


[33 


o 


Z in in ~* -* 


in 


^ >*<*-* 


^ 


^-\ 


CO 


O D. -H d CO 4-1 


w 


fO 




> 














to 


u 




rH 


3 3 CO 


H 




















CO 


x: 


T3 


rH 


o bo d 


















M 






o o u <f <r 


CM 


r^ r~. t~~ r^ 


(0 


bO 


U 


tu to 


,Q d o 


a 


4-1 




o^ O U vD o 


r^ 


O o -H ^ 




•H 


CO 


,a bOT3 (U -H S 


& 


C P 


* 


OO 0^ /-N 00 00 


C3^ 


0^ ^ ^\ ^ 


: 


CU 


>. 




tu Pi d tu 


o 


a; 0) 


CO ^ 


A 1 


4-1 










4J 


S 




o in 


•H d T3 


1 


e a 


-a r-l 


O CO 










x: 




U 


4-1 • 


a • M tu 


1 


cS 


>> 


m oj 










bO 


>^-rl 


f-~i 


• 




00 










•H 


Xi 


X3 


13 


ex d x: 


<! 


















(U 




3 


tu 14H 


to O tu 4J 




















>. 
















3 




O 


4J O 


•rl 4J 


X 


n 


















4-1 




CO 


CO 4-1 CO (X 


M 


T3 0) 


f 


< o o o o 


O 


o o o o 


>. 


d 


p 


a 0) 


CO CO IH 3 


Q 


4-1 


4J 


Z in in o <:»■ 


in 


O >* vO vD 


M 


(1) 


<u 


•rl 4J 


3 CJ CO 


§ 


r-4 -H 


O XI 


00 en o\ in 


o 


m o CO r~ 




B 


o. 


4J CO 


•H & 


u 


CO C 


x: --1 




*. as 


•> *s 






- - - 




tU 




CO IH 


00 rH tu 0) 


0^ 


4-> 3 


CO 


00 ^ vO CO 


CM 


r- -H in in 




o 


M 


CU 


CX t» IH 


Pi 


O bO 














r-H 


• 


1 


(U 


73 


(U CX CO 


■3 


H 
















bO 

to 


(H 
(L) 


4J 


<» tu 


rH to CM 3 

CX cr 




























► /^N 




• ^^ • 


^^ • 


/->. 


^^ • • /'^ 


XI 


4-1 


3 


d 


B rH bo to 




T3 






> CO 




• en • 


CO • 


CO 


CO • • CO 




J? 




0) a; 


CO CU d 




C 






c 




• c • 


e • 


C 


C • • C! 


c 


3 


X2 


^ 1 


C« 3 iH O 




CO ' 






0) 




. (U . 


OJ • 


(U 


(U . . 0) 


o 




rH 


3 B 


O M 4-1 




CO 











• B • 


e • 


B M S • • S 




(U 




bO O 


U 3 




C CO 


CO 




•H 




• T-t • 


n-l • 


•H tt) • t-l • • -H 


c 


boo 


•rl O 


. 4J -TJ 4J 




CU O 


60 




y 


> ^v U /-s 


O -^ 


O 14-100 U • • O 




to 


O 


14H 0) 


CO o 




S iH 


CO 




OJ 


• C (U c 


0) C 


tU M-l ^-\ 0) • • OJ 


• o 


U 


CO 


IH 


4J to -o .c 




•H 


XI 




a 


• 3 O- 3 


O. 3 


o< 3 OJ a. • • D, 


0) x: 


0) 




to 


d T3 OJ to 




O C 






CO 


• bO CO bO 


CO bO 


CO .a C CO • 'CO 


iH CO 


> 


bO -H CO 


to d w 




<U 3 






*v-^ 


» — / ^-/ s»^ 


^— / N--/ 


^^ N—' O ^-^ • • ^ 


X3 


10 


d 


,d r 


rH tu CJ to 




O, 00 


















N • • 


CO 4-1 




•H 


4J U 


CO 1 tu CO 




CO 




< CO O C3^ CO CM 


CO vO 


— 1 r^ CO < < CO 


r-l d 


d 


B 


a) 


tu a rH 3 








Z 








—1 Z Z 


•H 0) 


CO 


3 


- u 


CO O rH 




















CO 4J 

> d 




CO 
CO 


4J 3 
CO 4J 


CJ o 

-a <u CJ HI 






. 














4-1 




rH (U 


4J 


o o o o 


O 


o o o o 


to o 


CO 


to 


3 O 


d) u d 




Cd 4-1 


J= 


o in 00 -* 


o 


o <r vo o 


o 






"O to 


M CO O 




4-1 •!-( 


bOXi 


O CO vO 00 


o- 


P~ O CO o 


u 


•o 


•a 


14H 


OJ (H U N 




O C 


•H .-1 




*« •. 


n » 


•> 




- ' ►: 


O 0) 


(U 


<u 


d 3 


Xi 0) CO 




^ a 


<U 


<y\ — 1 r^ CO 


CM 


00 -H in vol 


z e 


4-1 


4J 


a| 


•rl p T3 d 




s 












f—t 


3 


to 


to 


HH 3 O 




















rH 


y~^ 


,-H 




•u -a •H 

tu CJ d 4-1 




». 
















< o 


3 


3 


x: 




u 
















z > 


o 


O 


bO bO 


M CO 3 -H 




box: 


















r-l 


rH 


•H d 


CO MH O CO 




CO M 


XI 


< O O O O 


O 


o o o Ol 


CU 


to 


CO 


X! -rl 


3 .fi d 




m -H 


i-i 


Z m in vo vD 


in 


vO vD 00 OOl 


X! 


o 


O 


to 


00 d 0) CO 




0) 
















• 4-1 






>^ 3 


eg (H p 

TJ g 4J 




3 
















1-1 


tu 


(U 


r-l 




















CO CO 


Vj 


u 


(U T3 


d -d 1 






















to 


4J 


< o r^ 00 <a- 


00 


in ~a- r~ in 


•H 0) 


^ 


^ 


B <U 


CO CO M 




bO 


O 


Z 00 CM CM vO 


<r 


-* 00 vo r^ 


4J N 


3 


3 


(U 4J 


. j3 a) 




(0 


x: 


.-H ^H 




^H .-H 


d -H 






u to 


m iH i4H 




PQ 


CO 














(U r-l 


to 
tu 


CO 

tu 


4-1 r-l 

X 3 


0) O 14H 

CO P rH 3 






















1 


» 














•H 4J 


iH 


•H 


tu CJ 


4J 3 .43 




U CO 


C C 














MH 3 


4-1 


4J 


rH 


CJ *J -d 




o u 


O -H 


< CO O O 00 


o 


in o CM] 


d 


•H 


•H 


(U to 


3 O d 0) 




Xi 3 


•H 


Z oc 


vO r~ 


CO 


-* 


m 1 in in| 


O : 


4J 


4-1 


X! CJ 


•d CO to 'd 




en -O 


4J 














O (U 


d 
to 


d 
to 


4J 

to 


O <4H •H 








/— «^ 








• 




i • • • 


M 3 CJN 3 








X 












» • • • 


>> 3 


3 


3 


O CO 


a d 1 








•H 












. .t~v • 


d 1-1 


cr 


ir 


4-1 3 


S CO -u 

(U B <U <4H 




(U 




f 












• • .--nC-^ 


CO O 










r-l 














« • H-l /-N 


(X > 


M 


M 


bO u 


T-i r-i 1 




a. 




4-1 












• O X3 


B 


tu 


tu 


d <u 


CX >, cxo 




e 




OJ 












• -H 


o >^ • 


4J 


u 


•H 4-1 


^ e rH 




CO 




3 












• u u 


O PQ U 


CO 


CO 


is 


cO CO ^ • 




!/) 


















: tU 


:s 


s 


en 4-1 w <! (U 


















t^ 


r^ 


<~i 4-lcsJ no Jt- LD LD COt^ CO C 








CO -^ 


in vc 


l-~ 


00 


<y 


cr. o O 


O CO 








0) o 
























^H ^H 


U 3 








4-1 N 



59 



< 

I 

H 
Q 

W 



M 

<! 
I 
I 

• 

pa 

X 

H 
Q 
Z 
Cd 



o 
o 



y-i bO 

•H @ 

u 
-a • 

3 w 

C 

CO 0) 

•H 

^ 
CO 

4-1 ^^ 
03 

3 m 

13 U 
0) 

iH iH 

to & 

u a 
o rt 



> 
H CO 

o -u 

H 05 

a 



o ex 
^§ 

4-1 0) 
03 

3 4J 

T3 M-l 

0) K 

CO S 

M O 

•H T3 

03 C^l 

oi >, 

J3 



bO 
>. 

■C CO 
(U M 
U 0) 

O rH 

(U o, 

r-l B 

i-H CO 

o 0) 
o 

4J 

4-1 y-i 

03 -H 
S M 
t3 73 



CO O 

4J ta 
o 

H 



CO M 
<U 4-> JS 



'4-1 
CO 
W3 



bO 



en v£> CO 
in r-. cvi 
vO vo O 



o 00 00 
r^ r^ o 
r- r^ o 

• • • 
o o 



O r-- r-. 
o^ <n o 
r^ r^ o 



<3 O < 
Z Z Z 



Z Z Z 



<3 < <j 
Z Z Z 



CO ro O 
00 \i3 c^) 
lO uo O 



■< <; << 
Z Z Z 



<3 <d < 
Z Z Z 



u~l \D --1 
CM CO — < 
O O O 



<r CM o 

vo r^ ON 

• • • 

<r CO I 



CO cfl CO 

z z z 



O CM CM 

<r «;j- o 
00 00 o 



CT\ r-~ 00 

CO UO --I 

I— I .— * o 



^ CM 0^ 
CO vO vO 

-* CO o 



r~. -si- CO 
O o o 
t-^ p-~ o 



vO vD O 
^^ 00 CO 
CO CM O 



1—1 CM —I 
CM CM O 
-* <t O 



<r ■<}• 



CM 00 -a- 

CO --I -H 
CM CM O 



CO 00 m 

CO CO O 

r^ r^ o 



CO CO CO 

z z z 



r^ m CM 
>* ~* O 
^ -vl- O 



00 in CO 

CJ> 0^ O 

r^ r^ o 



-vT -4- o 
~a- r«- CO 



■<f -* O 

O vD -^f 
■* CO o 



CT^ r-- CM 

o o o 

-3- >:f O 



-J- CM CM 

r^ .-H v£> 

.-H ^H O 



<t -^ 



vO CM sD 
Cvl CO O 
\0 \D O 



O ->J- v£) 
vO CO cs) 
vD VD O 



CO CO CO 

z z z 



r--. .-I vO 

vO vO O 

in in o 



ON 00 ^ 
f— I 1— t o 
00 00 O 



00 CO in 
o o o 
in in o 



vD vO o 

r~ <■ CO 
o o o 



(NJ NJD V£> 

.-I 00 CM 
CO CM O 



CTN —I CM 
\D r~ O 

<yi ON o 



<}• -vT I 



&. D-CM 

<; <c CM 

z z • 

o 

+1 

in 



(1> Q,\D 

<J <! m 

z z • 

+1 

CO 
O 

• 

00 



<j <; <3N 

z z • 

i-H 
+1 



P- CXCvJ 

<! -^ o 
Z Z • 

+1 

CO 



9- a.m 

<! -"Sj in 

Z Z • 

>* 

+1 

CO 

in 



&< 0< ON 

<! <; CM 
z z ♦ 

+1 

in 



z z 



+1 
in 



<j <; ^ 
z z • 

+1 

CO 



P, d CM 

<3 <J CO 
Z Z • 

+1 
o 



00 >3- vO 
in 00 CM 
1— I in -* 



o vj -* 

!->. -H ~j 

in vo o 



o o o 
CM ON r^ 
CJN r--- 00 



vo CO r~ 

O CO vO /^^ >^> 

in in ON CO ro 



O Cvj CM 

vD r^ --H 

CO vO CO 



O r-. CO 

-* CO o 

-^ •<)• O 



ON in v^ 

ON vo ^ 
f-H CM o 



CO O vD 
-H CM 



00 O CM 
CM O CM 

-H in CO 



vO O -3- 
CM ON ON 

r-» CO vo 



CO in CM 
o in in 
in CM r-^ 



ON in \D 

vO O CO 
o -H o 



00 O CM 
CM ON vO 
cvj v£> <t 



on tT) CO 



CO vO CO 

CM 1-H ON 

CO CM 00 



r~ in 00 

O '^ CO 
O O O 



p- 00 ^ 

CO 00 in 

vO vO O 



^D in ON 

vD CO \0 

in CM so 



-<r ^ o 

^ CO CM 
ON O -H 



r~. O CO 

•^ --H VO 

00 r^ 00 



CO CO o 

ON CO -a- 
in -H in 



•<f CM 00 

CO r^ CO 
in -;r <JN 



r-. r-. o 
00 ON --I 
in <j- On 



ON ■<}• r-~ 
r>. CM -* 



in <JN -* 
in o in 
CO 00 -d- 



O o O 

ON -H CM 
\0 .-H -vT 



~a- r-- CO 
in 00 CO 

CO vO CO 



CO o P-- 

^ m CO 

in \£) r-l 



O r^ r^ 

--H On 00 

ON CO r-. 



nD CM vO 

<r r^ CM 

ON <JN o 



in 00 CO 

On in NO 

in CO p~ 



00 00 o 
CM in CO 
in -^ vo 



NO vO o 

o o o 
r~ O CO 



-^ CO CJN 

vO -* r^ 

^ CM O 



<r -3- o 

— I CM 1—1 



CO CM 00 
^ CM 



-* CM 00 
-H CM 



CO 00 in 

■^ vD CM 
-4- CM 00 



-* NO CNJ 

CM CM O 

CO in CM 

• • • 

•<r o NO 

^ Csl 



in CO 00 

^ vO -^ 

NO 00 CM 

• • • 

CO CM ON 

r-l CM 



<! CO <1 

Z r^ Z 

p~ 



in (3N -vT 

CM vO -^ 

r^ in 00 



O -^ -* 

O CM CM 
CO p^ -* 



in CM r-» 

O ON 00 

i-H CM rH 



CM O 00 
CNj CO o 

in r^ csl 



O <3- •<(■ 

in CM P-. 
00 in NO 



-3- ^ NO 
-H CM 



CM CNl O 

<r <JN m 
St 00 -d- 



-4- cjN in 
00 ~a- NO 

^ 00 nO 



CO in CM 

o o o 

CO CO O 



mom 

ON ON ON 

r^ ON i-H 



c^ <J- m 
00 o •-• 
00 ^ CO 



m p~ CM 
00 NO 00 

00 ^ CM 



CO p^ ~* 
CO m CM 
^H p^ m 



O CM CM 

no m ON 
<r 00 CO 



CM 00 NO 

00 ON r-l 

-H CO CM 



•<!• rH vO 



• 4-1 
4J ^ 

X3 bo 
bO -H 
•H 0) 



• •• 4J J3 

• /— \ j3 bO 

• CO bO -H 

• 00 -H 0) 



4J 00 



0) 03 03 
U O 



ac: 



(U » 
0) 03 

u o 



. •• 4J J2 

• ^ X! bO 

• CO bO -H 

• 00 -H 0) 

• ~^ 0) & 
4J C7N S 4-) 
03 • — 0) 03 
3 rH M O 



J3 bO 
bO -H 
•H <U 



N.-' Dh Pu Q s_/ pn p^ 



(U 03 
1-1 O 

CU CM 



• CO 

• 00 

■W CO 
0) ^ 
3 CO 
Q ^ 



4-) X 

J= bO 
bO-H 

•H (U 
<U IS 
S 4-) 
01 03 
M O 

Pm Cl, 



• CO 

• 00 

4J <!■ 

03 -^ 

3 CO 

Q --^ 



• 4-1 

4-> J3 

JC bO 

bO-r-t 

•H 0) 

0) > 

0) 03 

M O 

Cm cm 



4J 4-> <f 
03 ~^ 
3 CO 



CO bO 



bO 

4-1 
03 

o 

p^ ( 



J3 bO 
bO-H 
•H OJ 

» 4-t 
(U 03 03 
M O 



• CO 

• 00 



• o 



Oi CM Q 



3 CO 



4-1 J2 

J2 bO 
bO-H 

d) ts 

0) 03 03 

M O 3 

Pm CM Q 



rH S -U 4-1 



CO 



m 



NO 



bO 
C 

•H 
Wl 

3 
•T3 

0> 
4J 

o 

<U 



O 
O 

CO 
O 



4-1 

03 

3 

03 

•i-t 



03 

3 
t3 



bO 
0) 



•O '4H 

QJ 
H 03 





4J bO 
O -H 
Z Q) 

4J 
CO 03 

z o 



•H <u 

rH U 

a, o 
a.i4H 

CO 0) 

4J 

O 4J 

z xi 

bO 

•H 

<! S 
Z 

M 
0) 



CO 03 

H -H 
•H 

CO : 

> -Ul 

CO JS 
bO 



li. 



J3 


C 


bO 


3 


•H 


m 


0) 


H 




^ 


IHCO 


(X 




en 




3 


• 


C 


C 


1 


o 

•rl 




4-) 


•u 


CJ 


J3 


3 


bO 


3 


•H 


14H 


0) 


^ 


4-> 


1 


03 




O 


o. 


O. 


s-x 


3 




CM 


dcM 


3 




M 





60 



APPENDIX C.~GUNITE PORE VOLUME, DENSITY, AND POROSITY DATA 





Dry 


Satu- 


Length 


Radius 


Bulk 


Wt of 


Core 


Vol of 


Poros- 


Core 


wt. 


rated 


of core. 


of core. 


volume , 


sat sol. 


density. 


sol, cm^ 


ity, 




g 


wt, g 


cm 


cm 


cm^ 


g 


g/cm^ 


(pore vol) 


pet 


1 


163.80 


184.70 


7.20 


1.9 


81.66 


20.90 


2.01 


20.90 


25.59 


2 


190.78 


209.30 


8.00 


1.9 


90.73 


18.52 


2.10 


18.52 


20.41 


3 


172.31 


186.15 


6.99 


1.90 


79.274 


13.84 


2.11 


13.84 


17.45 


4 


168.39 


184.23 


6.99 


1.90 


79.274 


15.84 


2.12 


15.84 


19.98 


5 


134.11 


161.74 


6.97 


1.90 


79.047 


27.63 


1.69 


27.63 


34.95 


6 


158.45 


178.26 


6.96 


1.90 


78.93 


19.81 


2.00 


19.81 


25.09 


7 


159.27 


178.63 


6.97 


1.90 


79.047 


19.36 


2.01 


19.36 


24.49 


8 


143.65 


167.14 


6.98 


1.90 


79.161 


23.49 


1.81 


23.49 


29.67 


9 


164.35 


180.71 


6.90 


1.90 


78.25 


16.36 


2.10 


16.36 


20.90 


10 


172.37 


187.07 


6.96 


1.90 


78.93 


14.70 


2.18 


14.70 


18.62 


11 


171.53 


186.77 


6.98 


1.90 


79.161 


15.24 


2.16 


15.24 


19.25 


12 


172.96 


188.56 


7.03 


1.90 


79.72 


15.60 


2.16 


15.60 


19.56 


13 


168.95 


185.28 


6.98 


1.90 


79.161 


16.33 


2.13 


16.33 


20.62 


14 


0) 


0) 


0) 


0) 


0) 


0) 


0) 


0) 


0) 


15 


121.78 


127.84 


5.46 


1.90 


61.92 


6.06 


1.96 


6.06 


9.78 


16 


94.75 


95.49 


4.05 


1.90 


45.93 


.74 


2.06 


.74 


1.6 


17 


157.20 


165.30 


7.06 


1.90 


80.06 


8.1 


1.96 


8.1 


10.1 



^Defective sample. 



APPENDIX D. —PERMEABILITY DATA 



61 





Sleeve 


Time, 


Inlet 


Average 


Height , 


Volume , 


Permeability, 


Core 


pressure, 
psi 


s 


pressure, 
psi 


pressure, 
psi 


cm 


cm^ 


10"^ darcy 


1 


185 
185 


368 
376 


108-126 
103- 84 


117 
93.5 


0.7 
.7 


0.01386 
.01386 


3.45 




4.23 




185 


306 


84- 84 


84 


.7 


.01386 


5.78 




185 


360 


104-114 


109 


.7 


.01386 


3.79 




185 


380 


104-118 


HI 


.7 


.01386 


3.52 




185 


342 


106-108 


107 


.7 


.01386 


4.07 




Av... 4.14 




180 


151 


90- 91 


90.5 


2 


.0396 


Std dev... .86 


2 


28.2 




180 


147 


91- 89 


90.0 


2 


.0396 


29.2 




180 


145 


88- 86 


87.0 


2 


.0396 


30.6 




180 


159 


86- 88 


87.0 


2 


.0396 


27.9 




180 


138 


86- 90 


88.0 


2 


.0396 


31.8 




180 


141 


89- 89 


89.0 


2 


.0396 


30.8 




Av 29.75 




180 


1,900 


80 


80 


1 


-0198 


Std dev... 1.42 


3 


1 10 




180 


1,401 


80 


80 


X 

1 


.0198 


1.50 




180 


3,695 


80 


80 


4 


.0791 


2.28 




180 


2,294 


80 


80 


3 


.0594 


2.75 




180 


3,620 


80 


80 


4 


.0791 


2.32 




180 


2,270 


80 


80 


3 


.0594 


2.78 




Av 2.12 




180 


451 


80 


80 


-x 


0S94 


Std dev... .68 


4 


14.02 
15.05 




180 


420 


80 


80 


■J 

3 


.0594 




180 


425 


80 


80 


3 


.0594 


14.87 




180 


413 


80 


80 


3 


.0594 


15.31 




180 


548 


80 


80 


4 


.0791 


15.38 




180 


680 


80 


80 


5 


.099 


15.49 




Avg 15.02 




180 


62 


78 


80 


S 


099 


Std dev... .054 


5 


169.50 
173.09 




180 


85 


78 


80 


7 


.138 




180 


86 


79 


80 


7 


.138 


171.07 




180 


89 


79 


80 


7 


.138 


165.31 




180 


88 


80 


80 


7 


.138 


167.18 




180 


88 


80 


80 


7 


.138 


167.18 




Av 168.89 




180 


1 17 


80 


fiO 


7 
7 


.138 
.138 


Std dev.. 2.88 


6 


125.56 
122.42 




180 


J. X / 

120 


79- 81 


80 




180 


120 


79- 81 


80 


7 


.138 


122.42 




180 


121 


78- 82 


80 


7 


.138 


121.41 




180 


121 


79- 81 


80 


7 


.138 


121.41 




180 


122 


79- 81 


80 


7 


.138 


120.42 




Av 122.27 




180 


215 


80 


80 


7 


.138 
.138 


Std dev... 1.78 


7 


68.43 
66.87 




180 


im 1. J 

220 


80 


\J\J 

80 


/ 

7 




180 


243 


80 


80 


7 


.138 


60.54 




180 


243 


80 


80 


7 


.138 


60.54 




180 


245 


80 


80 


7 


.138 


60.05 




180 


242 


80 


80 


7 


.138 


60.79 




Av 62.87 
















Std dev... 3.74 



62 



APPENDIX D. —PERMEABILITY DATA—Continued 





Sleeve 


Time, 


Inlet 


Average 


Height , 


Volume , 


Permeability, 


Core 


pressure, 
psi 


s 


pressure, 
psi 


pressure, 
psi 


cm 


cm^ 


10"^ darcy 


8 


180 
180 


507 
727 


80 
80 


80 
80 


2 
3 


0.039 
.059 


8.30 




8.68 




180 


1,210 


80 


80 


5 


.099 


8.69 




180 


1,676 


80 


80 


7 


.128 


8.79 




180 


809 


80 


80 


3 


.059 


7.80 




180 


1,888 


80 


80 


7 


.138 


7.80 




Av 8.34 




180 


860 


80 


80 


7 


.138 


Std dev... .045 


9 


16.93 




180 


397 


80 


80 


3 


.059 


15.72 




180 


936 


80 


80 


7 


.138 


15.56 




180 


536 


80 


80 


4 


.079 


15.52 




180 


941 


80 


80 


7 


.138 


15.47 




180 


955 


80 


80 


7 


.138 


15.25 




Av 15.74 




180 


614 


80 


80 


4 


.079 


Std dev... 0.60 


10 


13.67 




180 


1,048 


80 


80 


7 


.138 


14.01 




180 


1,031 


80 


80 


7 


.138 


14.24 




180 


457 


80 


80 


3 


.059 


13.77 




180 


1,059 


80 


80 


7 


.138 


13.87 




180 


1,051 


80 


80 


7 


.138 


13.97 


"^ 


Av 13.92 




180 
180 


1,174 
,537 


80 
80 


80 
80 


7 
3 


.138 
.0594 


Std dev... .20 


11 


12.56 




11.77 




180 


1,061 


80 


80 


6 


.118 


11.91 




180 


1,255 


80 


80 


7 


.138 


11.75 




180 


781 


80 


80 


4 


.079 


10.79 




180 


1,353 


80 


80 


7 


.1386 


10.90 




Av 11.61 




180 
180 


1,829 
3,644 


80 
80 


80 
80 


2 
5 


.039 
.099 


Std dev.. . .67 


12 


2.31 




2.90 




180 


4,684 


80 


80 


7 


.138 


3.16 




180 


1,131 


80 


80 


2 


.039 


3.73 




180 


2,186 


80 


80 


4 


.079 


3.87 




180 


2,722 


80 


80 


5 


.099 


3.89 




Av 3.31 




180 
180 


1,273 
2,404 


80 
80 


80 
80 


4 

7 


.079 
.138 


Std dev... .064 


13 


6.6 




6.12 




180 


1,312 


80 


80 


3 


.059 


4.81 




180 


1,725 


80 


80 


4 


.079 


4.88 




180 


436 


80 


80 


1 


.019 


4.82 




180 


2,563 


80 


80 


6 


.118 


4.92 




Av 5.36 




180 
180 
180 


2,652 
2,500 
2,500 


80 
80 
80 


80 
80 
80 


1 
<1 
<1 


NA 
NA 
NA 


Std dev... 0.79 


15 


<1.0 


16 


<1.0 


17 


<1.0 



NA Not available. 



NOTE. — There are no data for core 14, which was defective. 



APPENDIX E.— COST DATA 



63 



Sample 



Fiber type 



Mfg. 
cost per 
bag 



Bag 
wt, 
lb 



Bags per yd^ 



By 
vol 



By 
wt 



Cost per yd^ 



By 
vol 



By 
wt- 



Admixture 
costs per yd^ 



l2 

2^ 

32 

4 

5 

6 

/•••••• 

8 

9 

10 

U 

12 

13 

14 

15 

16 

17 



Steel. 
...do. 



.do. 



AR-f iberglass .... 
...do 



Steel^ 

. . .do^ 

E-f iberglass 

AR-f iberglass .... 

Steel 

...do 



None 

Polypropylene. . . . 
AR-f iberglass .... 

Steel 

None 

Polypropylene. . . . 



NAp 
NAp 
NAp 
$3.05 
6.95 
3.49 
3.49 
4.69 
4.25 
3.80 
3.80 
2.70 
3.40 
4.25 
3.80 
2.70 
3.40 



NAp 
NAp 
NAp 
50 
50 
60 
60 
50 
60 
80 
80 
80 
60 
60 
80 
80 
60 



NAp 
NAp 
NAp 
68 
47 
54 
54 
54 
45 
41 
41 
41 
45 
45 
41 
41 
45 



NAp 
NAp 
NAp 
74 
74 
74 
74 
74 

61-2/3 
46-1/4 
46-1/4 
46-1/4 
61-2/3 
61-2/3 
46-1/4 
46-1/4 
46-1/4 



NAp 
NAp 
NAp 
$206 
330 
188 
188 
253 
191 
156 
156 
111 
153 
191 
156 
HI 
153 



NAp 
NAp 
NAp 
$226 
514 
258 
258 
347 
262 
176 
176 
125 
210 
262 
176 
125 
157 



NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
NAp 
^$143 
5l41 
^141 



NAp Not applicable. 

^Assuming a cubic yard of applied gunite weighs approximately 4,000 lb and contains 
3,700 lb of solids and 300 lb of liquid. 

^Types 1-3 contain silica fume, an accelerator, plasticizers , and a superplasti- 
cizer and employ a curing agent. See table 18 for cost estimate. 

^ Price per bag is f.o.b. plant, purchased in volume. This price was quoted for 
mining customers. Single-bag, over-the-counter price is $5.75/bag. 

^This cost derived by taking 917 lb cement/yd^ (manufacturer's specification) 
gal/94 lb cement x $4.18/gal of styrene butadiene. 

^This cost derived by taking 907 lb cement/yd^ (manufacturer's specification) 
gal/94 lb cement x $4.18/gal of styrene butadiene. 



X 3.5 



X 3.5 



64 



APPENDIX F. —TOUGHNESS INDEX DISCUSSION 



The proposed toughness index was in- 
tended to be a dimensionless number 
indicative of the fiber's contribution 
to the flexural strength; however, the 
selection of an appropriate denomina- 
tor in the toughness index equation is 
still in question, is sparking contro- 
versy among fiber producers, and will 
require careful resolution by the Ameri- 
can Concrete Institute (Committee 544) 



before the index can be meaningfully 
used. 

At present , the toughness index is 
calculated as the area under the load- 
deflection (L-D) curve out to 0.075 in or 
0.10 in, depending on the author, divided 
by the area under the load deflection 
curve of the fibrous beam up to the 
first-crack strength: 



„ , .J area under L-D curve to 0.075-in deflection 

Toughness index = ^ 7—=; — t- z \ ' 

area under L-D curve to first crack 



The toughness index is not standard- 
ized as it should be. The difficulty is 
caused by the disparity of index values 
obtainable by the different fiber config- 
urations. Short, straight fibers with 
high surface areas (rectangular in cross 
section) can be mixed in gunite in volume 
percentages up to 2 pet (approximately 
265 lb/yd ^) without impairing the work- 
ability seriously. At these loading 
rates, the fibers will increase first- 
crack strength (the equation denominator) 
to such a high value it reduces the prod- 
uct toughness index seriously. 

Long, deformed fibers, on the other 
hand, can only be used in low volume 



percentages, in the 0.4 pet range (ap- 
proximately 50 lb/yd ^) if workability is 
to be maintained. Accordingly, first- 
crack strength would be somewhat lower 
(making the equation denominator small) 
and the post-first-crack strength higher 
(making the equation numerator large) and 
giving a very high comparison value. 

The use of a denominator containing the 
first-crack value of a plain, fiberless 
mix of the same proportion used in the 
fibered product would provide a better 
measure of the fibers' contribution to 
the matrix. 



^U.S. GPO: 1984-705-020/5040 



INT.-BU.OF MIN ES,PGH.,PA. 27649 



4 



4 



H7b- 854 



^' J'^--. 










^'^^ *!m^^ -^^ ^°''-^;rr°^ ^■^'''.^i';z^'"\ o°".^%"°o ,^^ -• 















o « ■> -^* 




■o5 ^ 







^0^ \5, *7*l^^4' A 








• V*x A'' *'J^<1.^^<" .A. A »• R S • "p. ^^ fc 





-^^^t^V ., "v^^\/ V**->'^°' %'^»":^'\^^ 



A> 







%\..^/^i'°- .A^>^^\ c,°^^^%>o /\c;^/\ 

,40 - - - - ' 










J-"'*, 















* 







^^^°^ 














9' ,, '^^,^^:^'\#'' "o^*^-^/ >^,^^7^-y^ \.*^^'^%o'^ V 












**'% 



\^i 






^*. o 






^bV" 






<^°^ 



I < v« '^ 



.^^°- 







:^ >. c.-?^" *i 








7, ^^'3 















**'\ 






.-^^ \!.^.#^*.^^ 




V 



.0' o"""*, "O. 



.-5l" 




vr , 






















'^^^ 






"oV 









/..i^>>o .,/Vi.;^^"'^.. .oo^^.^^^o ./\ci^/\. co 











C,^*^^. 




I* -^^ "^ 







-.^^'V 
V ^ 











^ ^ ^"loL' 










^ * o « •> .^ 






>■ ' » « <?. (V - O N , 





















HECKMAN 

BINDERY INC. 



,^^ JAN 85 

N. MANCHESTER, 
INDIANA 46962 








^^^^ 




'bV" 















